I wasted 90 minutes in today's lab troubleshooting an issue that the IOS told me might cause the issue to begin with. I upgraded my 2821 lab routes to a newer IOS 15 version so that I can lab some Gatekeeper scenarios. I knew about this problem in the past but by default, the newer IOS versions (at least voice specific) enables a configuration to prevent Toll-Fraud. It's called ip address trust authenticate which requires that all IP addresses that attempt to place calls to a gateway be added to a list that allows the call to be place.
Now while I knew about this I figured it wasn't enabled since I already had configured my router and looking in my running-config this command was no where to be found. I went ahead and issued the no ip address trust authenticate command under the voice service voip configuration and sure enough I could place H.323 calls again.