pardon my ignorance, but I am not sure what this program is for. If you are calling a service number or if the service is calling your phone, aren't you charged airtime on your phone anyways? Or is this really a way to get international calls cheap or free using standard local airtime?
Ok, I'll try to explain.
With Betamax (like VoipBuster, VoipRaider etc) it is possible to call over ip. To achieve this there are a few options. One option is to use a real voip phone (which can be configured to use VoipBuster)
Another option is to dial a service number. When you call this servicenumber you'll get a computer which asks you for the number you want to dial. VoipCall simplifies this by showing all the contacts and being able to dial the contact directly (using the service and a small trick)
The call to the servicenumber is charged by your phone provider. The international call from the servicenumber to the recipient is charged via your VoipBuster credits.
I'm investigating the option to let the service call you and the contact. With this all the calling is charged on your VoipBuster account. For now this is impossible unfortunately so it's only interesting if you want to call to foreign numbers.
note: instead of VoipBuster you can also use a different Betamax reseller.