International calling card services are cheap to implement. The main issue people run into is fraud. I think that after DNS reflection, SIP attacks have to be o

International calling card services are cheap to implement. The main issue people run into is fraud. I think that after DNS reflection, SIP attacks have to be one of the most common assaults. In addition, I've never seen a prepaid calling company that didn't get defrauded, you just build the losses into your margins. The typical way this is is done is to get a carrier route to a specific country and then arbitrage between that rate and the expected rate from say AT&T. There's usually a lot of margin when you compare it to AT&T costs, but you'll find the business is ultra competitive. We call voice the race to zero.