I have this problem with a small NBX V3000 R6.0.14 system.
On outgoing or incoming trunk calls I have no voice path. On the incoming call I get an autoatt, dial ext, get transfered to that extension, I see a caller ID on my 3com phone, but no voice path to the outside caller. Same thing on outgoing calls, connection established, but no voice path. Internal calls work fine.

I have only four loop start trunks and I tested all four ports, they all have the same problem.
There was no work done on the system for a long time. It just stopped working recently.

Does any one have any idea what this might be?