I have tried this before about 5 months ago and found the same issue. I had hoped that by now Cisco would have fixed this issue.
I have a 3825 currently running 12.3(11r)T2 as our voice gateway that has two PRI's terminated into it for PSTN access. We have an Astrix environment for our SIP calls with ATA's on our remote sites. Other sites have a router with FXS ports and analog phones doing H323.
The issue is when I try to upgrade to 12.4(15)T6 or any other 12.4 IOS the SIP voice will not work but the H323 voice is fine?
Has anyone else had this problem and found a fix? Any links to fixes?