I think I saw the tip here--can you avoid this problem by setting (for example in the PAP2) "Answer calls without register" to yes?

This comes back to the early days of using the test account and setting the CID to spoof my home number but incoming calls failing. (Set "username" to the spoof number, but use "Auth ID" with the actual account phone#...)

The point is, this move is sensible for the Residential system. I assume you do not plan on supporting Asterisk for Residential accounts--Asterisk users will have to subscribe to the Carrier service, correct?