Yesterday, Apple officially released the new iPhone OS 3.0 software update, which supports a slew of new features including the long awaited push notification and “catch-up” features such as support for MMS and tethering. Unfortunately, AT&T has said that MMS won't be available on their network until “later this summer” and that tethering will be available eventually.
However, some bright minds have found a way to enable tethering on your iPhone right now, without jailbreaking. Just point your iPhone browser to http://help.benm.at/help.php and you can download and install a new configuration file for your iPhone and carrier. I tried it, and it worked! I was quickly able to setup a tethered Bluetooth connection on my Windows 7 laptop.
How do you enable tethering?
Once you locate the correct configuration for your carrier, download it directly on your iPhone, then reboot your iPhone. When it starts up, go to Settings > General > Network and you'll see an option to enable tethering. Once you've done that, you can establish a tethered connection with your PC or Mac via either USB or Bluetooth. Surfing the web is actually not bad on 3G.
The same site also has the settings for enabling MMS, but I haven't been able to find where to enter them.
Note that you enable tethering at your own risk. AT&T and other carriers may charge you for additional usage, if they figure out how.