Firewall/NAT

Hello,

I have the following setup:  Cbeyond's Cisco IAD with NAT disabled<>Public IP<>Monowall<>LAN/Switchvox Asterisk Box/Phones

I'm working on troubleshooting an issue with Cbeyond's sipconnect service. 

When my switchvox starts up it registers with the CBeyond SIP servers on outbound port 5060, then at some point (typically after a few outbound calls or inconsistenly 5-10 minutes) it reports that all circuits are busy.  When this happens cbeyond's logs show that somehow it's switched from outbound port 5060 to a random port typically 40000 - 60000.  Because if this port change outbound calls fail until we reboot and try all over again.

When i look at the firewall states on the monowall i only ever see the connection on outbound port 5060 and never see the 40000-60000 ports that they see on their side. 

The switchvox (asterisk box) is set to only communication on outbound port 5060 and Cbeyond is trying to say that it's the monowall that's switching it 40000-60000, but i'm not seeing this in the firewall states.

Am I missing something?  Is it possible that the monowall could be doing this?