As expected, Apple and AT&T have barred Vonage's international calling app from VoIP over 3G/EDGE. When you're out of Wi-Fi range, it instead redirects your call to local access numbers, where you're charged AT&T minutes as you access Vonage's rates.
On the iPhone, Vonage calls can be made by dialing in the app, or from your imported address book—but you need to have the app open. The BlackBerry version only works over the voice network, and the iPod touch version is obviously limited to Wi-Fi.
Available now, the app is only pay-as-you-go for the moment. Support for Vonage World subscribers is expected by the end of the year. The limitations suck, but it's better than the outright rejection that Google Voice received. [Vonage via New York Times]