I've had numerous customers reporting the same problem to me. VoIP.ms has offered numerous suggestions, none of which have been effective. The important point is that these same customers didn't used to have the problem. I have no doubt that the problem would cease if I were to port the customers to a different provider. That is not my goal, however, at some point the customers are going to become impatient and instruct me to do whatever it takes to permanently resolve the situation.
The problem of of the incoming caller not being able to hear the party who is answering the call at my customer locations only last 2 - 5 seconds and it appears to affect somewhere around 2% of the incoming calls.