When we reported that iPhone OS 3.1 breaks MMS and Tethering hack, we had many readers reporting that MMS and in some cases even tethering is working for them after upgrading to iPhone OS 3.1. It looks like it is working for users who had used the MMS hack.

Aaron Krill who had discovered the MMS hack for iPhone OS 3.0 is at it again. He has figured out a way to enable MMS on iPhone OS 3.1 without the need to jailbreak your iPhone.

Before you start, you need the following things:

• Modified version of ATT_US.ipcc (carrier file), which can be downloaded from this link.
• iPhone running iPhone OS 3.1
• iTunes 8.2 or iTunes 9

Note: This will work only for AT&T customers.

You then need to enable IPCC updates for iTunes 8.2 (or iTunes 9) and copy the carrier (.ipcc) file to your iPhone. To achieve this, you need to follow these instructions:

Enabling IPCC Updates for iTunes 8.2:
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%iTunesiTunes.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%iTunesiTunes.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.

Based on feedback from our readers and this HowardForums thread it looks like updating your iPhone with the carrier file is working for quite a few users. However, it doesn’t seem to work for everyone. Aaron thinks that this is because AT&T is in the process of removing the opt-out codes. I think AT&T is probably rolling out the MMS feature gradually for the official launch on September 25.