I have the following issue. I have a small number of 7911G IP Phones connected to a 2811 router. When I try to place a call between the IP Phones (virtual PBX) they ring out but when the user tries to answer the phone the microphones are mute(d). If I try to place a call to the outside world (the router is a gateway to a PSTN network connection) everything works fine. Also if I place a call to a phone linked through an ATA 186 (I have a small number of those also) it also works properly. Could someone suggest on where to find the cause or kindly direct me to some documentation that would help me solve this issue? Thank you!