I would use FastAGI whenever possible. You can even seperate the FASTAGI processes from the Asterisk box to run on another machine. Regular AGI can only support a few callers at a time.
What are the caller limits of regular AGI? I’m running dual xeon 3ghz with 4 gig dram on Redhat EL4. This is an exclusive Asterisk box.
I’ve been looking into the Areski_AGI php application for prepaid calling cards as a base for my external Oracle DB development. It seems to be fairly robust and hopefully stable.
Have you looked into that app at all?