The registration for your personal phone number at the 25C3 is now up and running. Excerpt from the eventphone page:

If you want to create a phonenumber for one of the upcoming events, you have to sign up first and give yourself a username.
You will get an email to confirm your account. Then you can choose a phonenumber for your cordless phone.
That is all you need to phone other people at the event for free. You can make friends or retrieve them, when they got spread over the whole area.
If you already have an account for you only have to click login.

Currently you can create phone numbers for the following events:

* 25C3

You can find more information about the Phone Operation Center in our public wiki