What are the recommended settings to successfully implement VoIP over 3G/4G data connection? Assume we are talking about using Polycom phones, and the 3G/4G data connection comes from a Cradlepoint router that is plugged in with AC power and has high gain antennas. The device will be stationary, so we will not have to worry about tower handoffs breaking the connection. This will be for fixed wireless aiming at a cell tower. I assume packet loss will be a big concern as we have no control or QoS abilities. Plus, the speed fluctuates so much. I have read to use G.729 codec, and TCP for signaling to bypass firewalls. Besides that, what other settings are recommended? Changes in MTU? Changes in voice payload ms? Is there a better codec to use? Header compression?