TecTel:
I used 204.11.192.23 as the IP (as I'm in the Eastern US). When setting up the SIP URI. You use the 777 number as the logon and the Phone SIP Password entered on your user page.
You do not need to setup a SIP URI for every number you purchase from them, just the 777 number. You then setup ICRs for each of the numbers you receive from them (i.e. 777xxxxxxx, 800xxxxxxx, etc.) and route it to where you wish. Don't forget to create ACRs with N"@callcentric.com".
I've had them for some time. Incredible price, however, goes unregistered sometimes. Requires a switch reboot. Set the Registration Expiry to 3 mins as this seems to help. I've setup DoNotCalls routes as well as others without problem. Also, providing you have the bandwidth, set the codec to G711. They can handle it, it's more efficient and the call quality is better.
Hope this helps. Take care...
Drew