When I call out off-net - the phone (say my cell) rings. But when I answer the call - my 7965G keeps ringing - not recognizing that the call has been answered. I am connected to the PSTN via a SIP trunk with XO Comm. I can't reach anyone there to try and troubleshoot. Wanted to throw it out to the Experts here if they have a thought what this issue might be,. Thanks.