The Macrumors web site is reporting that some users of the iPhone have suddenly discovered that AT&T WIFI access via the iPhone is free in hotspots such as Barnes & Noble and Starbucks. When attempting to access WIFI, the iPhone users are presented with a special login screen to which they enter their phone number and upon validation receive free WIFI access. This access only applies to iPhone users with an AT&T account (jailbroken phones on other carriers are not able to access free WIFI without an AT&T phone number).

Link: Macrumors: AT&T Providing Free WIFI Access to iPhone Users