Prepaid calling system

Hi Everyone

Hi, I would like to start a small prepaid calling card business where a user dias in from a pstn line to my voip gateway then the Asterisk authenticates the the call and forwards it to its destination (usuall oversears). My question is does this open source Asterisk + a digium voip gateway provide all that it necessary to do this? ie,
Calling card pin number generation+billing+ivr+radius all under windows?

Can someone suggest a digium voip gateway model number?