[Freeswitch-users] Does FS supports speex with ptime=40?

I am testing making calls with x-lite 4. Although it doesn't send a ptime in its INVITE/SDP, i can see it is sending RTP using ptime=40 as I can count 25 UDP packets per second. When I try to bridge this to PSTN which responds with PCMU, at the PSTN side I hear trembling/metallic/robotic audio. I was suggested to set FS to use ptime=40, so I've tried setting codecs with speex@8000h@40i But it doesn't work. I get: "488 Not Acceptable Here" (Reason: Q.850;cause=88;text="INCOMPATIBLE_DESTINATION) So it seems only ptime=20 is supported as listed here: http://wiki.freeswitch.org/wiki/Codecs#Transcodable_codecs Could mod_speex be changed to work with ptime=40 too? Or is there anything else that i can try? regards, takeshi