AT&T iPhone Unlocking Experience
I bought an iPhone 4 at the Apple Store in December 2010. At that time, the iPhone in the US was only available locked, from AT&T. My AT&T Locked iPhone came with the 03.10.01 baseband, which can not be unlocked with UltraSn0w. So, for nearly two years, I used my iPhone as an iPod Touch, tethering to my N900.
When I heard that AT&T would unlock out-of-contract iPhones, I was delighted, and immediately called AT&T’s Customer Service number to ask them to put in a request. When I reached a representative and explained my situation, she explained that in order to have my phone unlocked, I needed to have an active account with AT&T. I said thank you and hung up. Five minutes later, I called AT&T again and got another representative. She put in a request to Apple to unlock my iPhone. I thanked her and hung up.
This morning, I got an email from AT&T titled “Subsidy Device Unlock Request”. Excited, I put my T-Mobile SIM into my iPhone and plugged it into my MacBook. I opened iTunes and I saw this:

Finally. Now if only T-Mobile had the 2100 MHz band to support 3G data on the iPhone. But I’m happy with at least being able to use my iPhone as a phone now.