How to enable MMS on the iPhone OS 3.1

Apple and AT&T are promising to give iPhone owners MMS on the 25th of this month, but if you can not wait that long here is a way to get MMS on your iPhone now, this hack as even unlocked tethering for some users as well.  Aaron Krill discovered an MMS hack for the iPhone OS 3.0 and figured out a way to enable MMS on the iPhone OS 3.1 without having to jailbreak, check out the steps below.  This does not seem to work with everyone at the moment, especially iPhone 2G users. If it does not work the first time around try giving it one more go. But do it at your own risk, it may void your iPhone’s warranty.

To enable MMS on your iPhone you need to compete the following (NOTE: this will work only for AT&T customers):

- Modified version of ATT_US.ipcc (carrier file) that can be downloaded here
- iPhone running iPhone OS 3.1
- iTunes 8.2 or iTunes 9

Then you need to enable IPCC updates for iTunes 8.2, or iTunes 9, and then copy the carrier (.ipcc) file to your iPhone. Below are the instructions on how to do this:

Enabling IPCC Updates for iTunes:
iTunes 8.2 or iTunes 9 won’t allow you to apply the carrier file updates so you need to follow these steps:

MAC OS X:
1. Close iTunes.
2. Open Terminal (Applications > Utilities > Terminal).
3. Run the command: defaults write com.apple.iTunes carrier-testing -bool TRUE

Windows 32 Bit:
1. Close iTunes.
2. Go to Start then Run and type CMD.
3. Run this command(If you right-click on the cmd window you can paste): “%Program Files%\iTunes\iTunes.exe” /setPrefInt carrier-testing 1

Windows 64 Bit:
1. Close iTunes.
2. Go to Start then Run and type CMD.
3. Run this command(If you right-click on the cmd window you can paste): “%Program Files%\iTunes\iTunes.exe” /setPrefInt carrier-testing 1

Updating your iPhone with the Carrier file:
To update your iPhone with the carrier file follow these instructions:
1. Open iTunes & connect your iPhone.
2. Click on your iPhone in iTunes(under devices listing).
3. Windows Users: hold shift and click “Check for Update”. MAC OS X: hold alt and click “Check for Update”.
4. Select the .IPCC you downloaded earlier.
5. Reboot your iPhone.
6. MMS should be enabled on your iPhone.

[Source: iPhoneHacks]