Hello, I have the following idea, I would like to design an IVR system as well as call processing to do the following that I will describe, can someone please offer suggestions on the proper, and / or most effecient way to accomplish what I am trying to do?

E.g. Code the call processing into dialplan, AGI script, or perhaps something else that will be just 
as good.

Here is what I would like to do.

1.  Create a calling card system that will accept multiple incoming calls and conference them together.
2.  Use a database to keep track of customers ect.
3.  Need a billing system that will keep track of minutes used from each user in the conference.

I was thinking of coding this all in an agi type script with a utility called adhearsion, its a 
Ruby Gem that allows you to handle all call processing and database integration in one package very
easily.  

Please, any suggestions will be most welcome.

Regards.