From the AT&T site:
iPhone OS 3.0 Software Apple® iPhone™ users, get started with Wi-Fi
If you purchased an iPhone 3G S or updated your original iPhone or iPhone 3G with the latest Apple iPhone OS 3.0 software here's how to access AT&T Wi-Fi Services:
- Activate Wi-Fi from the settings icon on your iPhone.
- Once you are in an AT&T Wi-Fi Hot Spot, select "attwifi" from the list of available networks.
- Every time you enter an AT&T Wi-Fi Hot Spot, you will be automatically and securely logged into the AT&T Wi-Fi network.
- Enjoy surfing at broadband speeds.
Finally, a reason to go to Starbucks.
And before you ask, Macworld explains why this is a big deal:
Last year, AT&T granted its iPhone-using subscribers free access to what’s now 20,000 McDonald’s, Starbucks, airports, and other locations in AT&T’s U.S. hotspot network. But the process of logging in was tedious. At the hotspot, you had to enter your phone number, receive a free SMS, and then click a link to gain access. (App developer Devicescape made this process much easier via its Easy Wi-Fi apps.) iPhone OS 3.0 automates that process, not just for AT&T but for non-U.S. carriers who include Wi-Fi access in their plans.
As soon as you’re in range of an AT&T hotspot, the iPhone logs in and switches to the network. AT&T was so excited about dumping its terrible old method of logging in that it even issued a press release. The carrier says that there were 4 million smartphone connections at its hotspots in the first quarter of 2009—and I’d bet that most of those were iPhones. (Here’s AT&T’s motivation in making it easy to use its Wi-Fi network: Every byte of data that moves from the cellular network to Wi-Fi reduces cell network congestion, making the overloaded cell network function better for everyone else.)