A variety of iPhone users are are reporting that new MMS features have been enabled on their handsets in advance of AT&T's official start date of September 25.

Apple added new MMS support to iPhone 3.0 to allow users to send pictures, video and audio recordings, contacts, or locations from Maps via 3G-capable iPhones. However, use of the new feature requires operator support.

AT&T, apparently afraid that millions of new iPhone 3.0 users would completely ransack its existing MMS service, reportedly decided to put opt-out service codes on all of its iPhone users' accounts until the company could beef up its network to accommodate the new demand.

In announcing its plans to enable the feature for iPhone users, AT&T explained, "It was important to give our customers a positive experience from day one. We support more iPhone customers than any other carrier in the world so we took the time necessary to make sure our network is ready to handle what we expect will be a record volume of MMS traffic. We truly appreciate our customersâ patience and hope they'll understand our desire to get it right from the start."

Rather than turning on MMS service for millions of American iPhone users all at once, AT&T has been selectively activating users across the country. Once activated, iPhone 3G and 3GS users should see a new "Cellular Data Network" menu item within the General/Network page of the Settings app and a new camera icon within the Messages app for sending photos.

It's possible to install a modified carrier bundle for AT&T to activate MMS software features, but this does not necessarily result in functioning MMS. Without AT&T removing your opt out, MMS messages will queue up with a red exclamation icon as they fail to actually send.