had good luck with AT&T
There's a lot of bad info in the comments to that article.
I ported my AT&T number (of 10-15 years) to Straight Talk early last year.
Then late last year, I requested they unlock an iPhone 4 that was about two years old.
(I'd gotten it broken , from a friend)
I did identify myself as a former customer, and they processed the unlock within a few days.
In January, a friend got a used iPhone 4.
He identified himself as a recent AT&T customer, and they took care of him.
There is a documented (sim swapping) trick to avoid the iTunes backup/restore proceedure to set the phone to unlocked.
Ya just have to look for it (quicker & easier, too).
When I ran my iPhone locked (to AT&T) on Straight talk, I was Jailbroken and used an application to modify the settings so MMS would work.
But when unlocked, the iPhone 4 can be persuaded to let you edit the settings.
(on the 4S, this sim-swap trick works locked or unlocked)
Ya just have to look for it.
