AT&T has confirmed it will offer the Personal Hotspot functionality starting March 11 with the release of iOS 4.3, but it looks like the functionality will be modified to work only with connections up to 3 devices. By default, Apple's Personal Hotspot allows up to 5 devices to connect to a single iPhone sharing its 3G connection. A picture of an internal AT&T document posted by Engadget in fact suggests the carrier is going to restrict the usage of Personal Hotspot to only 3 incoming connections.
While it's highly unlikely that you'll end up letting 5 people connect to your iPhone on a daily basis, it's still interesting to study the possibility of AT&T limiting a feature so heavily promoted by Apple. Guess carriers do have some kind of control on the iPhone, after all. (Personally, I'm just happy 3 Italia is going to keep Personal Hotspot free to use for every iPhone owner)
Update: the image shared by Engadget doesn't specify whether or not AT&T is simply following Apple's implementation of Personal Hotspot, which allows 3 devices to connect using WiFi. It's not clear from the leaked photo if AT&T didn't mention the additional Bluetooth and USB connections, or is really enforcing Personal Hotspot on 3 devices simultaneously.
From Apple's website:
You can share your connection with up to five devices at once over Wi-Fi, Bluetooth, and USB — with up to three of those connections using Wi-Fi.4 Every connection is password protected and secure. And it’s power friendly, too. iPhone detects when your Personal Hotspot is no longer in use and turns it off to save battery life.