The highlight of Apple’s announcement Verizon would carry the iPhone was mobile hotspot support in addition to tethering. While the iPhone on AT&T supports data tethering, the process took months and was bogged with delays. To combat Verizon, AT&T is being more lenient with its data caps and supporting Mobile Hotspot for iPhone users.
As of right now the personal hotspot feature is available publicly for Verizon iPhone users. AT&T hasn’t announced its intention to provide the same feature but there is evidence the carrier will do so in betas of iOS 4.3. Developers on the other hand have been able to beta test personal hotspot support on their GSM iPhones since the first beta revisions of iOS 4.3 were released by Apple.
Obtaining and installing a beta of iOS 4.3 isn’t enough to enable mobile hotspot support on your AT&T iPhone. In addition to your data plan, AT&T requires you to sign up for a monthly tethering plan which costs $20 – the same as Verizon’s mobile hotspot plan.
If you don’t have access to a Beta of iOS 4.3 and pay for tethering support on your iPhone, you’ll have to wait for the public release of iOS 4.3.