asterisk users - May 2004 - no incoming audio on outgoing sipcalls

I finally got sipgate.de working for outgoing calls. I can dial and talk 
to any destination supported by my account but I can't hear the other 
party.
My asterisk is behind a firewall router with forwarded rtp ports 
10000-20000 (which is also defined in rtp.conf) to the * server.  
Incoming calls work fine and on clients in the same network directly 
registered with sipgate.de there are no probs.

Any suggestions?


jo