GSM on CCC Event Blog

39C3: Telephony

Tue, 23 Dec 2025 06:00:00 +0000

TL;DR

Registration is open – register your number in Guru3
Don’t forget your phone (ISDN, DECT, GSM, SIP)
Remember batteries, charging cables, and CCC SIM card
There will be eSIMs for the GSM network
The dial-in number from outside is: +49 40 5730830 xxxx

Preparations for 39C3 are already in full swing. You have already registered more than 5,600 extensions. We are very excited. We would like to take this opportunity to provide some information about telephony at 39C3 and have compiled the following details on all the technologies you can use to participate in the Congress telephone network. As last year, there will again be a phone helpdesk to assist you with any issues you may have with the various telephone networks. You will find it at the shorter table to the left of the long POC table.

Registering extensions

As every year, you can register your extension(s) in GURU3. We offer DECT, SIP, GSM, call groups, applications, announcements, and special extensions. Please make sure you register your extension in the correct event. You do not need to register for analog or ISDN extensions. Registration has been open since 18 November 2025. Reservations for extensions expire on 24 December. Unredeemed reservations will then be returned to the pool.

DECT

To connect to the telephone network via DECT, you can bring your cordless DECT telephone from home. You can check whether your device works with our system in our wiki: DECT Phone Compatibility List. The necessary steps for setting up your extension can be found in the instructions for registering DECT.

There will also be EPDDI (EVENTPHONE Decentralized DECT Infrastructure), which means: The EVENTPHONE network from the conference – wherever you want it. At the hotel, at home, in the hackerspace, or on the train. You decide. If you have RFP & Router, you can find the documentation for integration here.

SIP

You can also connect to the telephone network using a SIP telephone or a SIP softphone. The access data will be displayed in Guru3 after you have registered an extension. You can also find an overview of tested SIP clients in our wiki: SIP Compatibility List. You will also find General SIP Configuration Instructions there.

SIP extensions cannot make calls to the public telephone network, but they can receive calls.

GSM

Mobile communications (2G/GSM, 4G/LTE, 5G/NR) will also be available again at 39C3. A 3G network will not be offered. Telephony is only available on the 2G/GSM network. Please bring your CCC SIM cards and mobile phones with you. New SIM cards are available at the Phone Helpdesk.

eSIMs 🎉 will be available this year.

The following frequencies will be used to operate the event network:

2G: 1800 MHz, possibly additionally 850 MHz
4G: 1900 MHz (band 2/25 FDD), 2300 MHz (band 40 TDD)
5G: 3700 MHz (band n78 TDD)

Using the mobile network with iPhones is somewhat problematic due to technical challenges. CCC SIM cards of a certain generation are not compatible with the event network in iPhones. The affected SIM cards in iPhones must be updated or replaced. You can contact the phone helpdesk for assistance.

For more information on mobile networks, keep an eye on @c3gsm.

Dawn of ISDN

This year, there will once again be a real ISDN network with an EWSD. An EWSD is a digital (ISDN) exchange by Siemens for public telephone networks, which was in operation between 1980 and today. We have reduced it to a minimum, will set it up at the Congress, and connect it to the PoC network.

To create some excitement, the theatre group has made a short video:

Visitors will have the opportunity to connect to the EWSD via ISDN or analog. For ISDN, if you have an NTBA, please bring it with you. If you don’t have an NTBA, you can borrow one from us. There will be access multiplexers at various locations in the event area where you can connect your phones or other devices. You can find the exact locations in the c3nav maps.

Each of the ports on these multiplexers is already configured. The first two cards in each multiplexer (with two large plugs) provide analog connections. The other cards (with one large plug) provide ISDN connections.

No extension registration in Guru is necessary for an EWSD connection. A fixed extension is already configured for each extension. Additional features such as charge pulse can be configured on request. Please contact the Phone Helpdesk for assistance. More information.

For EWSD information, keep an eye on @c3isdn.

Services in the Phone Network

The familiar services will be available on the telephone network again this year.

Would you like to meet other people? Dial 6528 for Blind DECT.
Don’t know your own phone number? Dial 8330 for ERNA.
Not sure which network you are on? Dial 0310

You can also link your phone number to your account in the Event Hub. To do this, you must enter it in your profile and confirm it. Once your phone number is connected, you can take part in the RFP Challenge, for example, to earn a special badge for finding DECT antennas. To do this, dial 9737 with your DECT phone.

You can find more information in the wiki: Special extensions

What else?

Up-to-date information on the status of our services is now available on our dashboard.

The external dial-in number is: +49 40 5730830 xxxx

With DECT, GSM, Premium SIP, analog, and ISDN connections, you can make phone calls from the event to anywhere in the world. Many thanks to Sipgate for this.

We look forward to seeing you in Hamburg. Don’t forget your phones. Whether analog, ISDN, DECT, or mobile. Remember batteries, chargers, connection cables, and your SIM card.

Thank you. Eventphone.

38C3: ISDN Version

Sun, 22 Dec 2024 16:00:00 +0000

TL;DR

Registration is open - register your extension in Guru
Don’t forget to bring your phone (DECT, GSM, SIP)
Remember to bring Batteries, Chargers und CCC SIM-Card
Our public dialin number: +49 40 5730830 xxxx

2024. The brave new world has completely transformed telephony. IP telephony has replaced conventional telephone technology, including ISDN and all its components. Until 2017, we drove a truck to the Chaos Communication Congress on December 21. We spent days hauling, packing, pulling cables, patching cables, configuring, maintaining main distribution plans and fixing errors so that everything was up and running by 26.12. at the latest. Then we registered every DECT phone by hand from 26.12. onwards. We were finished on 29.12. and on 30.12. we dismantled until the new year.

Over the past few years, we have packed our IP DECT system with features and optimized everything to such an extent that we have even laser-cut our own boxes for our hardware.

We have 3D printed logos for our DECT RFPs, a web server runs in the PoC dwarf and how it works is properly documented in the internal wiki. With screenshot. Translated with DeepL.com (free version) Boring! We arrive by car, someone pushes a computer into the rack, we distribute a few RFPs, connect them to the network and we’re done. Cabling? We don’t do that anymore. We’ve outsourced that to the internet manufacturer. Logging in? We no longer do that. We’ve outsourced it to the users. All the vintage technology is done by Chaosvermittlung. Last year, we took part in Hack Zuck on day one as a team. Because we had time. It couldn’t go on like this. We all realized it was five before total neglect. Tidiness was getting out of hand and before anyone™ had the idea of making art, someone else™ found a very large metal cupboard that was bigger and heavier than our old, rationalized telephone system. The metal cabinet goes by the name of EWSD, which means Electronic Dialing System Digital. And all like this: Yeah!

Back to ISDN

ISDN has been switched off. We’re switching it back on! And analog telephony too.

EWSD is a digital (ISDN) exchange from Siemens for public telephone networks that was in operation between 1980 and today. We have reduced it to a minimum, will set it up at the Congress and connect it to the PoC network.

Visitors have the option of connecting to the EWSD via ISDN or analog. For ISDN: If you have an NTBA, please bring it with you. If you don’t have an NTBA, you can borrow one from us.

For the complete retro experience, you can dial into the Internet via modem or ISDN. Of course with channel bundling. You’ll be surfing faster than you have for a long time!

It is not necessary to register an extension in the Guru for an EWSD connection, there are fixed extensions for this which are assigned locally. More Information. For EWSD information, keep an eye on @c3isdn.

Regisgter an extension

As every year, you can register your extension(s) in GURU3. We offer DECT, SIP, GSM, Callgroups, Applications, Announcements and Special Extensions. Please make sure that you register your extension in the correct event. You do not need to register for analog or ISDN extensions (see above). Registration has been open since 25.11.2024. The reserved extensions are reserved until 13.12. Reservations that are not redeemed then fall back into the pool.

DECT & EPDDI

It is our core product. Stable since 1993, always with the best network coverage¹ at the congress. In the underground car park, on the toilet or on the dance floor. If you can’t be reached on your DECT phone, it’s not because of Eventphone. Want to know if your device works with our system? Take a look at the DECT Phone Compatibility List.

There will also be EPDDI (EVENTPHONE Decentralized DECT Infrastructure), which means: The EVENTPHONE network from the congress - wherever you want it. In the hotel, at home, in the hackerspace or on the train. You decide. If you have RFP & Router, you can find the documentation for integration here.

GSM

There will also be mobile communications again at 38C3. There will be 2G, 4G and also 5G coverage. Bring your cell phones and CCC SIM cards. New SIM cards from the camp are also still available. For information on mobile networks, keep an eye on @c3gsm.

And what else?

From 26.12.2024, we will provide up-to-date information on the status of our services on our Dashboard.

Our public dialin number: +49 40 5730830 xxxx

With DECT, GSM, Premium SIP, analog and ISDN connections, you can make phone calls from the event to anywhere in the world. Many thanks to Sipgate for this.

We look forward to seeing you in Hamburg. Don’t forget your phones. Whether analog, ISDN, DECT or mobile. Don’t forget batteries, chargers, connection cables and SIM cards.

Danke. Eventphone.

also in selected hotels and areas of HafenCity ↩︎

C3GSM wants you to test yesterday’s future, today!

Sun, 22 Dec 2019 17:42:02 +0000

tl;dr: we will operate our own cellular network at 36C3. Bring your
mobile phone(s) and C3SIM card(s). Check the Wiki for latest status and device support.

Like previous years at 36C3 the C3GSM team will run a local cellular
network for mobile phones, alongside the
POC’s DECT system and the NOC’s IPv4 and IPv6 systems. As core network
for our cellular network we use the open source projects osmocom (for
2G/3G) and NextEPC (for 4G). There will only be a very limited number of
SIM cards available to buy. However, cards from previous CCC events can
be used, so please don’t forget to bring them.

As always, we had to ask commercial operators for permission to use some
of their parts of the spectrum, which unfortunately has been completely
sold to very few commercial operators.
We got permission to use 5 MHz of the 850 MHz band, which we will use
for 2G/3G and 10 MHz on the 2600 MHz band for 4G (LTE).

That was rather unfortunate news, as we cannot use a 2G or 3G frequency
which is common in Europe. As 850 Mhz is a frequency commonly used in
the US, some of you will not have a phone which can be used for voice
calls as we don’t support voice over LTE yet.

This also means that contrary to our plans (and for a first time since
many years), this year will not see full 2G coverage of the venue, so
that some very old phones may not work in our network at all.

If you have spare old phones, you are willing to donate to the public,
you are encouraged to throw them in our phone dumpster near the GSM
helpdesk. Remember to wipe all your personal data before and attach a
power adapter if not usb-esque.

Looking forward to route your calls and mobile data in Leipzig! For
questions and support visit the GSM helpdesk Also, we would like to hear
your feedback. Even if things don’t work as expected. Maybe especially
then! ;)

36C3 Phone registration is open

Sun, 01 Dec 2019 22:42:54 +0000

We are pleased to inform you that even with Resource Exhaustion the registration of telephone extensions for the 36th Chaos Communication Congress is open. Don’t get confused by the social media, it works without any voucher :-). You can claim your DECT, SIP or GSM extension in the Generic User Registration Utility (GURU). Like last year, you can register your devices on site yourself. Don’t forget your devices and chargers, chasing records, this year we want to break last year’s 6488 extensions.

Stay connected!

Mobilfunk auf dem Camp

Sun, 11 Aug 2019 11:20:00 +0000

Good news everybody. There will be a mobile phone network at the camp.
We will setup a 2G/3G network and experiment with 4G as well.

Our network will support general data and voice services. The mobile
network will be connected to the POC, IOW it’s possible to call between
DECT and GSM numbers as usual.

Number registration is done via the guru UI.

Additionally we’re planning to add an interface to send and receive SMS
over HTTP. So you can create your own SMS-IRC gateway!

You will need to use a congress or camp SIM card to connect to our
network, so please bring your SIM cards from previous events, for
yourself and/or to share with your neighbours. We will only have a few
spare SIM cards to sell.

Ring! Ring! #35C3

Fri, 21 Dec 2018 19:15:12 +0000

This year, we want to show that it is possible to provide reliable, secure communications infrastructure with the highest quality and premium service. For you!

DECT, SIP or GSM extensions can be reserved in the new GURU3. The old accounts and data from GURU2 have been migrated. It is now possible to select a random free extension or to display all free numbers at the push of a button.

Last year we wrote: “Unfortunately it is technically not possible to speed up or parallelize the process [of the telephone registration]“. And because it seemed impossible to us, we built it. We have retired our loyal old system and started to develop from scratch. With new hardware and new software – with focus on our biggest problems: How do we get rid of the long queues at the DECT registration? How to register phones in parallel? How can you register phones wherever you have DECT reception? How can everyone register their own phone?

And the DECT self-registration was finished. We tested it at Easterhegg 2018 with 250 users, twice. ;-) The next test took place in England: At EMF Camp already had some more testers and it worked without problems right away on the first attempt. At 35C3, we want to crack the 2500 DECT extensions from last year. Without queues! How does it work? We describe the procedure in a detailed article.

2502 DECT Extensions at 34C3.

Activate encryption in your GURU3 account and only deactivate it, if your phone does not work with activated encryption.

Our first tests have shown that considerably more devices work with the new system than with the old one. Unfortunately, there are still manufacturers that deviate so much from the specification, that it is not possible for us to integrate devices from these manufacturers. We maintain a list of compatible devices in our Wiki.

There will also be GSM (mobile radio) again this year. We still have some SIM cards in stock, but please bring SIM cards from previous congresses. They still work. The GSM team will expand the network to 1800Mhz (2G) and 850Mhz (3G). The constellations in which voice and data will be distributed have not yet been finalized.

Since there was too much abuse at past events, there will be no SIP dialout on the 35C3. The 20 outgoing voice channels are only available for DECT and GSM (mobile radio) extensions. A dial-in for SIP, DECT & GSM extensions will be available at +49 (0) 464438299 < Extension>. EPVPN extensions are available from the event network with the prefix 01999 and from the EPVPN the event is available with the prefix 09.

There are other small and large new features such as the telephone book via LDAP, ringback tones or hotel DECT. Furthermore, we have a new support system. Requests via e-mail, webchat, web form, telegram message or Twitter are collected in our helpdesk software, where they can be processed by several people. We hope to offer you an even better customer experience. :-)

Eventphone phone book via LDAP on iOS.

We will keep you up to date via Twitter on the @eventphone and @epstatus channels.

Goodbye,
the Eventphone Team

Phone infrastructure at 34C3

Thu, 21 Dec 2017 16:38:28 +0000

Needless to say, we will provide to you a phone infrastructure at Leipzig. Please do not forget to bring your DECT and mobile phone with you (and the correct charger, maybe even a headset if you have one). The congress is hosted in Leipzig for the first time, really the biggest congress location ever and maybe we have some unknown constraints. We are prepared for this big event with up to four system components (in Hamburg we had one) and up to 60 antennas (in Hamburg we had 45). We try our best to provide a comprehensive DECT network, but can’t promise because of the unknown building. If you want a fallback, register a SIP extension and use a SIP Client e.g. with your smartphone.

We apologize for the very long waiting times to register your DECT phone. Technically it is not possible to speed up or process in parallel, but we will try a new solution called PoC-Q. You can push a button and get a queue ticket. Via a website you can check your position in queue and the estimated waiting time. Hence you can use your valuable time with whatever you want instead of waiting in PoC Help-/ Registration desk line in the glass hall. If you want to find out if your DECT device is compatible with the POC-PBX, have a look on the DECT Phone Compatibility List in the Eventphone Wiki or send us a tweet (@eventphone).

What about mobile phone network (GSM/UMTS)? You can assume that there will be a GSM/UMTS Network but very experimental. The GSM team give everything to setup the mobile network, but we cannot estimate how big and which frequencies. At the PoC we will install a dashboard with the current network status and we push the important news via twitter. 5000 blank, unlabeled SIM Cards will be available and we sell them at the PoC (CCL Level 0) from 26.12.2017, 11:00 a.m. Update: You can reuse SIM-Cards from past chaos events.

DECT, SIP and GSM/UMTS extensions can be registered in the Generic User Registration Utility (Guru).

GSM and Phone Infrastructure

Thu, 22 Dec 2016 12:14:44 +0000

Good news: There will be GSM at 33c3! Bad news: There are no SIM Cards available! At the past events we spread thousands. Please bring your SIM Card(s) and share your SIM Cards.

To (hopefully) prevent so much questions during the very short setup time, here is our plan ™:

23.11. – Extension registration in GURU for 33c3 is open.
23.12. – Starting GSM setup.
24.12. – Setup the Eventphone PBX, hang up DECT antennas.
25.12. – 11:00 a.m. Start issuing preregistered orga DECT phones, rollout wired devices, registration of new orga DECT phones if (inter)network is working.
26.12. – 11:00 a.m. Start GSM extension registration in GURU, start DECT registration for visitors.
27.12. – 09:00 a.m. GSM, DECT, SIP, EPVPN & wired phone services are up and running.