Recently i tried to bring up a small experimental Softphone setup on linux.
Installed linphone on two different linux distros and tried to establish connectivity , worked like a charm ; voice clarity was pretty decent as well. The most interesting thing was to see the packets captured through tcpdump/ethereal , the SIP messages and then the RTP packets with 20ms worth of payload data ( valid for ulaw/alaw).
Calculation of packet size for G.711 ( two versions alaw/ulaw )
bitrate(kbps) * packet size(ms) = packet size (bytes)
This was my first experiment with voip , it went really well so im happy .