asterisk users - Sep 2004 - Incomming calls are fine. No sound on outbound.

This one is wracking me brain...

Trying to setup a Cisco 7960 in a friends office. We opened their firewall
to allow any ip traffic in/out that was comming from or going to our *
server.  The phone registeres itself with * fine. If I place a call from my
cell (or any other phone) to the 7960, both sides can hear perfectly.

If I try and call my cell (or any other number for that matter) from the
7960, the call rings, and the other side picks up and * shows that the call
is in an "open" active state, but neither party can hear the other.

It seems really odd that outside PSTN calls can come into the phone and be
heard fine, but outgoing calls to PSTN cannot be heard at all. I don't know
why it would be a firewall problem if the FW is set to allow all
incomming/outgoing ip packets.

Any ideas? What can I use to troubleshoot? Doesn't the conversation transmit
on RTP ports? They are open as well. All ports are.

Thanks,
Matthew