Han,
I think i may have come across this sort of issue before with my first use of the FreeSWITCH system.
Have you seen anything such as this in the logs/fs_cli output during the call?
2011-09-28 15:37:12.047658 [DEBUG] switch_ivr.c:577 sofia/internal/1000 Command Execute playback(/usr/local/freeswitch/sounds/en/uk/cg_test/cg_out_test_welcome.wav)
EXECUTE sofia/internal/1000 playback(/usr/local/freeswitch/sounds/en/uk/cg_test/cg_out_test_welcome.wav)
2011-09-28 15:37:12.047658 [DEBUG] switch_ivr_play_say.c:1302 Codec Activated L16@8000hz 1 channels 30ms
2011-09-28 15:37:12.107661 [DEBUG] switch_rtp.c:3181 Correct ip/port confirmed.
2011-09-28 15:37:12.317674 [WARNING] mod_sofia.c:1115 Asynchronous PTIME not supported, changing our end from 30 to 20
2011-09-28 15:37:12.317674 [DEBUG] sofia_glue.c:2775 Changing Codec from PCMA@30ms@8000hz to PCMA@20ms@8000hz
2011-09-28 15:37:12.367677 [DEBUG] switch_rtp.c:1527 RE-Starting timer [soft] 160 bytes per 20ms
2011-09-28 15:37:12.367677 [DEBUG] sofia_glue.c:2857 Set Codec sofia/internal/1000 PCMA/8000 20 ms 160 samples 64000 bits
I looked into this at the time and my understanding was that I need to try and add PCMA@20i in /usr/local/src/freeswitch/conf/vars.xml and re-compile however i have not revisited the issue yet as i only found this to be an issue with outbound only calls from FS, something i was doing just as a demonstration.
I found it can be resolved by updating my handset to set RTP Packet Size to 0.020 (its default was 0.030). I doubt this is of much help but perhaps its worth checking? This is my first contribution to the mailing list and i'm not a greatly experienced used but i did want to raise this as a possibility - apologies if this hasn't been of any use!
Thanks,
Callum Guy