ok, than try this:

edit h323plus/src/h323caps.cxx, grep it for "H323AudioCapability(240, 30) // 240ms max, 30ms desired" ... it should be at line 2598....

replace 30 with 20, recompile (make && make install) make sure you use the new compiled library and start FS.

let me know if you still have audio issues.