We have found via Cnet a new Wi-Fi hot spot feature: Auto-authentication on the iPhone OS 3.0 for faster connections.

This is good for the iPhone users who have struggled to access the free 20,000 AT&T Wi-Fi hotspots because of the steps used to do this. Auto-authentication allows iPhone users to switch from 3G networks to Wi-Fi hotspots without being prompted the new process, makes it easier and faster for iPhone users to connect to AT&T Wi-Fi (Autoconnect is established when a customer connects their iPhone for the first time.

You may still continue to access AT&T Wi-Fi using the current method although Auto-authentication is available to all existing iPhone and iPhone 3G customers using iPhone 3GS.