I just spoke with a Vonage sales agent about the Vonage iPhone app, and boy do I hope she was misinformed about some of the details:
1) It is not tied to your existing Vonage account. It isn't Vonage Companion for your iPhone and isn't associated with your existing Vonage number. You don't even need to be an existing Vonage customer or have an existing Vonage phone number to use the Vonage iPhone app.
2) The Vonage iPhone app will be geared/marketed towards the international traveler, allowing cheap international calls to be made over a WiFi connection. This would be something that competes with the cheap or prepaid long distance calling cards/service.
3) There will be more info provided to the public at the end of September.
Again, I hope she was wrong about it not being tied to your existing Vonage phone number for incoming and outgoing calls. Yikes! Vonage, please don't disappoint us!!!