Despite numerous hints about AT&T's plans to offer free Wi-Fi to iPhone users, AT&T has yet to make an official announcement and the service is currently unavailable.
The reason for the delay may simply be that they have not yet deployed their Wi-fi hotspots to all Starbucks locations. AT&T only recently took over Wi-Fi service from T-Mobile at Starbucks and it appears the transition remains ongoing. The photo above was taken today at a Starbucks in California.