I have a deployment of SPA504G phones in SIP mode against an Asterisk server. Often, when outbound calling, the first roughly quarter-second of incoming voice is cut off once the far end picks up. It sounds like it may be some sort of automatic gain control kicking in, but it can be annoying from a user perspective (I just saw a user dial someone, the far end picked up and said "hello?" within a quarter second of picking up, and the near end end heard nothing). Is this some sort of configurable behavior?
It's possible it's something with Asterisk's SIP RTP handling, but we previously had 7900 series phones talking to Asterisk via chan_sccp-b, and it did not have that problem.