Reports have been trickling in the last few hours via my email, IMs, etc that there is a new remote unlocking via IMEI available for all GSM iPhones. There have been a few forum goers mention they can do it, which seems a bit shady (no actual business, no way to get money back other than trust, etc). By far the most reputable we've seen though is Negri Electronics, whom we've known for years. They've been selling unlocked phones for years, and are trustworthy good folks.
Here's the gist of it - you pay someone $175 (that seems to be the going rate across everyone we've heard from), and send them your iPhone's IMEI. Within 24 hours, they send you an email saying it's unlocked. You then sync with iTunes, and your iPhone is unlocked. That's it. No codes to enter - you're just unlocked. It doesn't work with Verizon iPhones (they don't take a SIM card), and it doesn't work on any iPads. But any GSM iPhone - $175 for an unlock that won't care what firmware, update, or jailbreak status you're on. Just like a factory unlocked iPhone (which it basically then IS), it's unlocked for the life of the phone.
How does it work? Well - Apple has a database already which they query when you do a sync in iTunes to check your devices lock status. That's how it works if you call your carrier and they unlock the device for you - you sync in iTunes and it is unlocked. There is a source wholesaling remote unlocks, and many in the industry suddenly today picked up the ability to do this. It would seem someone with access to this db is basically selling that access - as far as my research shows, everyone who is selling this is getting it from the same source. This could be totally sanctioned and legit, or this service may just as suddenly stop being available one day (although once you've been unlocked you'll be so forever).
If you've got a need for this, and your carrier isn't going to do it for you - this is good news. I have not yet personally tested this, although the folks at Negri have, and my IMEI is in the queue to be unlocked, I will update this story tonight with my personal results. I would strongly recommend you stay away from random eBay folks and websites that are popping up to do this, and use Negri Electronics's service (same cost) if you're interested (no, we don't get a cut and we aren't getting anything out of recommending their service over others, ha). They've been around a decade doing this with a solid track record.
Again, I will update this story with my personal experience sometime tonight.
UPDATE: I received word back from Negri Electronics that my iPhone was unlocked. I synced in iTunes, and didn't get a "unlocked" message (only 60% of users do though). I am currently trying to find a non-AT&T SIM I can cut and install to verify the unlock. I do not have ultrasn0w installed on this iPhone, nor have I ever. I will update again asap when I can confirm.
Negri Electronics has also paused the service as they have had a huge response and the source has a queue of thousands of IMEI's. Once those have been processed, the service will reopen.
UPDATE 2: Success! I have verified my iPhone 4 is unlocked. It wasn't QUITE as simple as advertised - I wound up having to make sure I was updated to 4.3.1, and when I did iTunes told me "Congrats, your iPhone has been unlocked!" But I did no processing other than update to 4.3.1, and have verified the iPhone works on an active T-Mobile SIM. I do not have ultrasn0w installed, nor have I ever on this device. Here's a couple screenshots: