MacRumors reports that AT&T hotspots are now offering free Wi-Fi access to iPhone users.

Barnes and Noble, Starbucks and presumably AT&T’s 71,000 other Wi-fi hotspot locations are now offering iPhone users a custom portal to access free Wi-Fi. A special iPhone formatted page asks for your mobile phone number. Once entered, you can access the Wi-Fi access for free.

MacRumors has been able to confirm this finding at a local Barnes and Noble. Blurry photo provided:

AT&T recently partnered with Starbucks (displacing T-Mobile) to provide Wi-Fi access to Starbucks’ 7000 stores nationwide. This partnership allowed existing AT&T broadband customers free access and AT&T promised that it would “soon extend the benefits of Wi-Fi at Starbucks to its wireless customers”, but no official announcement has yet been made.

Even better – this functionality is based on the iPhone’s user agent – which is easily imitated with the browser on your computer.

We haven’t had a chance to give this a try yet. If you’re at one of AT&T’s 71,000 hotspots today, give this a try and let us know how it works!

Update: This service appears to have been disabled, at least for now. No official word on this from AT&T.