I have an interesting issue happening with a very small number of locations That i call. The issue is that If I call them or they call me, they can not hear me. Like I said this is only happening to a very few locations. Is they a setting I should look at that may need changed for a more compatible hand shake when Going from Voip to Voip.
If an incoming call from a problematic location is answered by Asterisk (IVR prompt, queue announcement, voicemail greeting, etc.), is that audio also not heard by the caller?
In the incoming INVITE for a failing call, which codecs are offered? Does Asterisk reply with the first one? If so and it sends audio to the correct IP address and port with proper packetization and properly formatted voice is indeed present, IMO there is nothing more to do at your end and Spectrum should look at the problem.