I have a customer with this same problem... internal calls to the QSC softphone work fine but it can't make external calls.  Were you able to resolve this?   Thanks, Kyle

Since this is a year old, you've probably already gone with a solution but I thought I'd chime in on this anyways.  Jamie has the correct answer to resolve the calls going to the cell phone voicemail...  You should then be able to modify the voice ma...

If you set this parameter to yes, the call is treated as a modem call. The ATA 190 tunes VAD, Jitter buffer, and echo canceler automatically.