If you checked for updates for your US-based iPhone in iTunes in the last day or two, you should have seen this:
The standard Apple explanation from the Knowledge Base:
iTunes 7.7 and later has the ability to update the carrier specific settings on iPhone with iPhone 2.0 software or later. Carrier settings updates are small files (about 10k) that are downloaded from iTunes to be installed on your iPhone. The carrier settings can include updates to the default APN (how iPhone accesses the carrier's cellular data network), special dialing codes at Settings > Phone > [Carrier] Services, default settings for Stocks, Maps, Weather, and other items.
So what's actually in this update?
Logo replacements, apparently, for AT&T's upcoming MicroCell service (at the time of this writing, the page is in maintenance mode). 2 images, light and dark versions of the image on the left (courtesy of MobileCrunch). Commenters at The iPhone Blog also confirm the revised connectivity image. Our own commenters note that Apple has added settings for the Mobily network (Saudi Arabia) and Etisalat (United Arab Emirates) in this update as well, which adds weight to the expected 2/15 launch of the iPhone in those countries.
Editor's Note: Canadian and European customers report no carrier update for them, which is understandable considering the AT&T-centric content of this update. To all of our international readers, if we got you all excited about this update, our apologies for your disappointment. With the exception of Jason, we don't have non-US iPhones to test with, so we often can't say for sure whether a specific update is universal or domestic-only.