Firewall/NAT

I have the following setup at 2 locations...cable modem->m0n0->VOIP Server and Lan Computers

I previously had a linksys router and had the ports for the VOIP forwarded to the VOIP Server.  I have tried to do the same in m0n0, I have forwareded upd 5060, udp 15000-15511 and TCP 8081 and UDP 2088 which are required by my VOIP server.  The VOIP Server at each location needs to communicate with the above ports to the remote voip server.  However after switching to m0n0 it does not work.  The VOIP server see each other and you can call from location to location the phone rings, but there is no voice or the firewall is performing some kind of non standard NAT.  The company that makes the voip server says that the firewall is not forarding the above ports correctly.  I have set approriate firewall rules and have made sure nothing is being blocked via the Log file.  Can anyone think of anyting else that i might try to get this working.  Thanks

If anyone is curious....I had to enable Advanced Outbound NAT and create an outbound nat route.  Then the VOIP worked fine. 

What is the VoIP server you are using ? Sounds weird.....

Disabling source port rewriting is required for many VoIP deployments, which is what Advanced Outbound NAT lets you do.