This is the method that has worked for us and a few others that we have confirmed solid—if you know of any shortcuts or another way to enable MMS, let us know in the comments. Update: If you’ve been having issues, Giz reader Justin adds some additional steps (now numbered 3 and 4) that he says has worked for him and several others. Let us know it goes.

What You’ll Need
• iPhone 3G running OS 3.0
• Another AT&T phone (non-iPhone)
• This carrier file
• SIM ejector tool (or paperclip)

Make sure that you have carrier testing enabled in iTunes before proceeding:

 Step 2: Press Windows Key + R to open the run dialog. Enter in cmd then click OK

Step 3: Enter the following command into the Command Prompt window.

“C:\Program Files\iTunes\iTunes.exe” /setPrefInt carrier-testing 1

Step 4: Connect your iPhone and click to launch iTunes from your Start Menu.

Step 5: Select your iPhone from the list of devices on the left then hold down the Shift key and click the Check for Updates button.

Step 6: Now you can now select your .ipcc file as it is not greyed out

Prep Your iPhone
1. Download the carrier file.

2. Connect your iPhone to your computer. Open iTunes, and option or ctrl click (depending on whether you’re Mac or PC) “check for upgrade” which will open up your file browser. Select the .ipcc file. This is just a carrier file, it doesn’t do anything to your OS or data. Uploading it to your phone will just take a couple of seconds.

3. To make sure the update worked, go to Settings->General->About and look for “Carrier.” It should say “AT&T 5.”
4. Then go to ettings->General->Network->Cellular Data Network. It should say wap.cingular in the APN box, WAP@CINGULARGPRS.COM in the Username and CINGULAR1 in the Password field. Reboot your phone (you can do this after you take the SIM card out).

The Workaround

5.Take your SIM out of your iPhone and pop it into a phone that’s capable of MMS. Make sure it’s registered to your account on AT&T’s site (go into your account manager), replacing the iPhone as your listed phone. You might have to do this manually. I made a couple calls with the phone to make sure it registered

6. Go here, to AT&T’s MediaNet site, and register your phone number. You’ll get an SMS with a 4-digit code to confirm. Punch it in at the website.

MMS, Baby

7. Put your SIM card back in your iPhone. MMS should be working now! It’s kind of pokey (about 30 seconds to send a picture) and it’s dropped a message or two, but we were able to send pictures to people on multiple carriers and receive video from a phone on T-Mobile. It definitely works, and works pretty well. The interface for playing back MMS video (pictured up top) is slick, too.

8. Wonder how you ever did without it.

Word of Caution

We’re rocking an unlimited family messaging plan, so we’re not worried about any charges for blasting out tons of MMS messages. If you’re worried about account weirdness, you might wanna hold off. You could always ask your local AT&T guy to make sure you’re not getting hosed, just tell him you’re a developer (you’ve got iPhone 3.0, after all). Also if you’re squeamish about unofficial OS files, obviously.

Big thanks to Scratic, who showed this method to us. If you know a better way, let us know!

©Gizmodo

Before you can follow these instructions you must have a jailbroken iPhone and you must be on the 04.26.08 baseband(modem firmware). This means that you must be running the 3.0 firmware and have used PwnageTool or RedSn0w to jailbreak.

To find your firmware and modem firmware(baseband) versions you can follow this tutorial. If you are not on baseband version 04.26.08 then you need to upgrade to OS 3.0 via iTunes.

If you are on T-Mobile remember to turn off 3G before starting…

Step One
Press to launch Cydia Installer from your SpringBoard.

Step Two
Press to select the Manage tab at the bottom of the screen.

Step Three
Press to select the large Sources button

Step Four
Press the Edit button at the top right of the screen.

Step Five
Press the Add button at the top left of the screen.

Step Six
Enter http://repo666.ultrasn0w.com/ as the source url and press the Add Source button.

Step Seven
Once the source has been added press the large Return to Cydia button.

Step Eight
Press the Done button at the top right of the screen.

Step Nine
Press to select repo666.ultrasn0w.com from the list of user entered sources.

Step Ten
Press to select ultrasn0w from the list of packages

Step Eleven
Press the Install button at the top right of the screen.

Step Twelve
Press the Confirm button at the top right of the screen.

Step Thirteen
After installation completes successfully press the large Return to Cydia button.

Step Fourteen
Now press the Home button then power off and power on the iPhone. You do this by holding down the power button for 3 seconds then moving the power slider that appears to the right. Press the power button again to turn on the phone.

Step Fifteen
You should now be able to insert the SIM of your choice!

***THANKS: A big thank you to all the members of the iPhone Dev-Team for all their hard work! It is much appreciated by all.

Download RedSn0wfrom here or here and place it in the Pwnage folder. Likewise, download the latest 3.0 firmware from below and place it in the same folder.

3.0.0 (3G): iPhone1,2_3.0_7A341_Restore.ipsw

Extract the RedSn0w zip file to the Pwnage folder.

Step Two
Connect your iPhone to the computer and launch iTunes.

Select your iPhone from the list of devices on the left. Now hold down shift and click the Restore button. Restore is preferred as it won’t create any wasted space on your iPhone.

Navigate to the Pwnage folder on your desktop and select the firmware ipsw. Click the Open button to continue.

Step Three
Once iTunes has finished updating your iPhone to the desired firmware you may launch redsnw0w.exe from the Pwnage folder on your desktop.

Step Four
Once RedSn0w opens click the Browse button

Step Five
Select the firmware ipsw we placed in the Pwnage folder on our desktop then click Open

Step Six
Once the firmware has been verified click the Next button to continue.

Step Seven
Make sure Cydia is selected and click the Next button.

Step Eight
Please plug your iPhone into the computer and make sure its OFF then click the Next button

Step Nine
RedSn0w will now guide you through the steps to get into DFU mode.

Hold down both the Home button and the Power button for 10 seconds.

Release the Power button and continue holding the Home button until RedSn0w detects the device.

Step Ten
Your iPhone will now reboot

Step Eleven
RedSn0w will then begin uploading the new RAM Disk.

Step Twelve
Once this is complete you will be notified that RedSn0w is done. Click the Finish button.
When your iPhone finishes reboot (5 minutes or so). It will be jailbroken with Cydia on the SpringBoard.

iClarified