Audio - What can I do when call is connected but I can't hear any voice? (RTP packets are empty)

In this case please check a gain of your DSP processor. You can do it by AT command at&v0. In the response of this AT command you can see parameter g01 which should have value 2,32,32. In case that you see value 2,0,0 you have to use at%g01=2,32,32 to set this parametr properly. This applies only for firmware 2.07.35b02 and lower.