From your very first post, you stated that OBi 110 DTMF detection works fine with connection to a ILEC POTS line. Correct? if so, OBi has no DTMF problem with regular PSTN network.
The problem appears when you have OBi device connected to an ESI PBX where QWEST is the ILEC.
Since digits go through QWEST VoIP network, we need to diagnose if any distortion is introduced in DTMF signal, particularly when the testing calls are originated from Verizon cell phone. If your PBX connects to a SIP trunk and all the digits (via RFC2833) are received OK, then, local generated digits should work for OBi device. However, if digits are actually sent as inband signal, speech vocoder might distort DTMF signal badly, e.g., G.729 as you pointed out (even G.711 will have some minor impact), which could be reason why OBi 110 cannot recognize those digits.
Please check with your service provider on whether this is the case, or it would be better that you have a test device to check on DTMF signal that connects to same PBX.
