A piece from the article that's out on Observer about Rebel calling:
Magnus Larson, CEO of Rebtel, told us this is the reason his company is launching Rebel Calling, a new way to call internationally that’s dirt cheap. Following today’s launch, Rebel Calling will actually be free for one year, but then you’ll be able to make unlimited international calls for only $1 per month, no WiFi required.
How it works is simple—both you and the person you want to call need to download the app and sync your contacts. Then, when you want to make an international call, make it from inside the app. Rebtel Calling will connect you and your foreign friend by making two local calls, essentially creating an international conference call.
Read the article at observer.com