When iPhone OS 3.0 was announced, it was going to support tethering, but whether you get tethering or not depended on your current carrier. Once the 3.0 software was released and officially supported tethering, even though AT&T wasn't ready, hacks emerged that allowed one to enable tethering, even if their carrier officially supported or not.
If you're not familiar with tethering, it's the process of using your phone as a modem to access the Internet on a laptop, usually via USB or Bluetooth, with the phone's current data connection (EDGE, 3G, etc).
Even though it's been only a few weeks since 3.0 came out, Apple has already began beta testing of iPhone OS 3.1 with developers, and beta 2 was released last night. However, reports are surfacing that 3.1 beta 2 disables the tethering hacks for AT&T customers.
AT&T will officially support tethering later in the summer, though it will come at additional cost.
