Short version: Vonage Mobile + iPhone = WIN!
A few weeks back I received an iPhone 2G as a gift. My wife and I had originally bought it for my father-in-law when the iPhone first came out. He lives in Toronto and had the phone jailbroken so he could use it on Rogers' cell network up in Canada. Somehow or another the phone's firmware got updated which killed the jailbreak on the phone and he could no longer use it on the Rogers network. Well, not being a very technical guy, he thought he broke the phone. He went out and got himself a brand new iPhone 3G S and gave the 2G to me.
He knew that I would figure out a way to get it working again and he was right. After I figured out what happened to the phone to begin with, I simply upgraded to the 3.0 firmware and jailbroke the phone. Well, I don't have AT&T. In fact, I'm a Sprint customer, so I can't use it as my cell phone. Once I hacktivated the phone, I went ahead and started using it as another iPod Touch. My 2nd Gen iPod Touch is only 8GB and this one is 16, so I loaded it up with music and put it in the car (my car's radio has an iPod cable). Well, I really like the iPhone and was trying to figure out a way that I can use this thing to make calls. There's tons of VoIP apps out there, but none of them gave me the clarity I was looking for. I even tried using the Skype app and while I sounded great to the person I was calling, they sounded like crap to me. Enter Vonage Mobile.
I've been seeing commercials for Vonage Mobile for a few weeks now. It talks about how low it's international rates are and I got to wondering how it would work for domestic calls. The info in the app store said nothing of domestic calls, so I downloaded it anyway to give it a shot.
Setup was simple. When asked for my iPhone's phone number, I entered my Google Voice number. It called that number to verify and it simply went to my Treo Pro. Once everything was up and running, I made some test calls to my wife and best friend. The sound quality was amazing on both ends and best of all, domestic calls are FREE! Granted, I can't use this thing as a "real" cell phone because Vonage only works over WiFi, but when I want to call someone that I don't want to have my cell number I can use the iPhone so they get my Google Voice number. It'll also come in handy when I'm charging my Treo Pro or something. I'll figure out a way to use it pretty often.
One thing that is cool about this is if you have the cheapest plan that AT&T offers for your iPhone, you can use Vonage to make your phone calls while you're at home or around a hotspot and NOT eat up your minutes! I don't think that Vonage is advertising that you can make free domestic calls from their app, so I just thought I'd pass the info along!
Also, if setting up QoS after you do this, the ports are 5060-5062.