We use a Verizon Business SIP Trunk, with 3845 CUBE 12.4.24T. CallManager 7.0(2) and 7962G(SCCP) handset. All calls have dynamic MTP and are G711.
Had the exact same symptoms again twice, only I was dialed out to 704-XXX-XXXX.
I hit the QRT button to record the issue.
The destination can still hear me but I can not hear them. Hang-up call back, all is ok. Then it happens, again an undetermined amount of time later in the call.