Full disclosure, this issue first started because I was unable to get the Cisco Mobile 8 iPhone app functioning when using the built-in VPN.
In the interest of troubleshooting a Call Manager / VPN / iPhone issue, I decided to install CUPC client on my Mac as it too is a SIP client very similar to the iPhone. The CUPC Soft-Phone does not work when I use the IPSEC VPN client. The app logs in but errors out when it tries to initiate the soft-phone and I get a constant "connecting" at the bottom.
Because the iPhone app is a SIP based phone in Call Manager as is the CUPC client, I am thinking it is a VPN / Firewall issue.
To be doubly sure (and to rule out a Call Manager issue), I installed Cisco's Any Connect (SSL) VPN client on the same computer. Interestingly, using the Cisco SSL VPN, the CUPC soft phone client works 100%.
At this point I am convinced there is an issue with the IPSEC VPN. Because the IPSEC VPN works for everything else but this voice app (on the mac and iPhone) I am stumped as to what the issue could be. Especially because everything is Cisco through and through. Cisco ASA 5510 hosting the IPSEC and SSL VPN connections, Cisco CUPC and iPhone apps......
I assume that as long as the issue with IPSEC and the CUPC soft-phone problem persists, the same issue will still prevent the iPhone app from working also.