Is iOS 7 Going To Bring Built-In VOIP calling?
iOS 7 is slated to arrive sometime this fall. At WWDC, Apple indicated that they would introduce audio only Facetime calls. At first it seemed to be a big "so what". Big deal, you could save bandwidth on a Facetime call. But, then on a second take that would mean that it would be the same as a phone call over wifi. Think Skype, but without a separate app. You will be able to access this right in your contact, the way you do with Facetime.
Now picture yourself in Europe on vacation and you want to call home. You simply open your contact, hit Facetime audio and your call goes through just like a regular phone call. The person on the other end doesn't have to have Skype open to receive the call like they used to.
Here is a nice article that talks more about how Apple is building this feature in very quietly.