Necesary to do VOIP prepaid cards:
Phone lines: As many as concurrent calls you will have.
Analog, plain lines or T1 or E1 if you are lucky to be able to get it and afford it.
If you are on the US, go for fractional T1 . will save you many headaches.
A gateway. Device that will do all the conversion from PSTn phone lines (analog or digital T1 to VOIP)
A permanent conection to internet. Static I.P. address a must .Several I.P. addreeses a plus, but not absolutely necesary.
A billing system. A software running on a small server or beefed up P.C., used to control the gateway and be the cash register of the bussines.
A big bottle of aspirin or advil and a very understanding wife or husband (do not want any complaints from the ladies).This is a must!!!!!!
Some help from someone that already went trought the process.If you do not have a friend that did, get one. There in no money that could pay the advice.
Good luck!!!!!!!