Greetings from Germany. Over here, the biggest carrier, Deutsche Telekom, is rolling out IP-based telephony to their mainstream customers via their VDSL package.
I was also pleasantly surprised that the connection now also comes with a IPV6 address that hopefully will solve the problem with the 24-hour IP address change on IPv4.
Anyway, the way the account needs to be set up is like this. Essentially you need three strings to register the account. Your telephone number, your email address and your password. The telephone number is the number in German area code notation, for example 03080282602, the email address looks like firstname.lastname@example.org and the password was just numerical in my case.
I wasn't so sure which number I needed to pick. I logged into the FritzBox, and checked out the Internet access credentials. The email address account (the text before the @) was stored in the access data ("Zugangsnummer"), and I just needed to put the "@t-online.de" behind it. The telephone number is in the account statement. I don't remember where I got the password number from, luckily I still had it somewhere.
We have added this to the drop-down in the SIP trunk setup page, so that you can set this up very easily from 5.2.6 onward.
We just forward all incoming calls to one account. It would also be possible to do this based on the MSN, this is just like all other providers. Also I had to make sure that the country code was set correctly, so that the numbers in the display make sense.
We'll keep watching this. Who knows, maybe IPv6 is next.