39C3: Telephony

39C3: Telephony

EN DE

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.