Inbound SIP no audio [outbound and zap r great]

asterisk 1.0.7

inbound SIP calls to my * server are generating no audio.
all outbound calls sip and zap are great
inbound zap is great

an inbound SIP from ipkall.com is working well also.

however (my two testing sources) an inbound SIP call from sipgate.de and an inbound SIP call from a pulver.communicator softphone both arrive at my * server.
I see the default dialplan executing, but neither client recieve any audio.

when using tethereal this the last line I see from teh client
SIP Request: ACK sip:s@<my server’s external IP>

what logs or configs could I post to help?

TIA
amccool

Do you have different nat settings for ipkall.com then you do for sipgate.de?

I am having the same issue with sipgate. Did you find a solution ?