Hi do have this Problem too.
I tried migrating a 2811 VSEC to 4331 VSEC and failed because auf IP inspect not present.
I then decided to go with ZBF but that Failed to because this router is a h323 gateway and after configuring ZBF i got working connections, but unidirektional voice streams, Phone -> Router -> ISDN is working, ISDN -> Router -> phone is not working.. I tried 3 -4 different ways, when I remove ZBF Voice is working as expected but I do not have that Firewall Feature for local Internet Breakout