I have a US iPhone 4 on 4.1 but still the 4.0.1 baseband (upgraded and jailbroken with TinyUmbrella and greenpois0n) and then unlocked with ultrasn0w. On a trip to the UK, I am using a "Three" data-only SIM intended for iPads, which I bought as an experiment for just ten pounds for 1GB/30days, and it works just fine for data and even incoming texts, and as I have My3G I can use Skype to make and receive calls, which is great. However, unlike with the original AT&T SIM, the FaceTime feature is nowhere to be found. There is no FaceTime button on a contact page, even when on Wi-Fi. Actually, now that I mention it, there's no Call button either (which is understandable as it's a data-only SIM). I'm amazed I can do as much as I can, but it would be nice if FaceTime worked too, especially as I'm going to Singapore next month and would like to do a similar thing there with a StarHub data-only Micro-SIM.