There are many various conflicting reports in regards to using an iPhone in the United States, so I thought I would set out a how-to that works for me. 1. Get your phone unlocked This means unlocked from your carrier, or with an easily available 'unofficial' unlock. Not jailbroken, that's a separate thing. The goal here is to make your phone work with a SIM card from any available carrier. 2. Acquire an AT&T pre-paid sim card. The iPhone uses the GSM network, so your choices for such in the US are AT&T and T-mobile. T-mobile does not support the iPhones 3G bands so you are going to be stuck on EDGE speeds on their data network. You have a few options to get a sim card: eBay before you arrive, or from an AT&T store/kiosk after you arrive (don't tell them you have an iPhone!) For the newer phones that use a micro-sim, there are tutorials online to cut down a regular one to fit, or you can buy a do-hickey off eBay. 3. Buy pre-paid credit You can use the website if you have a US credit/debit card. Or if you got one off eBay, I hope you bought one with included credit. The easiest method, though, is going to be to buy a refill card at pretty much any gas station/Walgreens/bodega. 4. Load carrier settings for AT&T. It's really important that you don't use your iPhones IMEI when activating the sim card. AT&T will detect it's an iPhone and you will bork it. I don't think there's any way to recover the sim and start fresh if that happens. So at this point you have a phone that will make and receive phone calls, but to access data services, you need to change a few settings in the phone. Step 1: Find a WiFi connection you can access on your iPhone Step 2: Visit http://www.unlockit.co.nz/ on your iPhone in Safari. Step 3: Select “Custom APN”. Step 4: Scroll down to “Carrier” and select “US – AT&T” or "US- Cingular" Step 5: Hit “Create Profile” Step 6: A screen will come up. Tap the blue “Install” button to install the profile. Confirm the next dialogue. Step 7: The profile will be installed. Re-start your iPhone and test the data connection. 5. You should now have a fully featured iPhone in the USA. As I said, this method has worked for me for years. I hope this helps, and I welcome any input.