Tutorial: MMS on iPhone OS 3.1 (AT&T)
http://www.krillr.com/blog/N72ZCXJH/tutorial-mms-on-iphone-os-31-att
 
September 10, 2009
 
If you like this tutorial and want to see more, follow me on twitter or make a donation.
 
Welcome to the newest tutorial on how to get MMS working on your AT&T iPhone! Keep in mind this tutorial is for users of iPhones running iPhone OS 3.1 on AT&T's network. The settings provided here may or may not work with earlier versions of the iPhone OS, and certainly will not work on any other network.
 
I believe the issue with you still getting the exclamation is due to AT&T's ongoing process of removing the opt-out codes. Slowly but surely everyone will be given access. Keep trying periodically over the next few days.
 
The first few steps are the same as before, we must enable IPCC updates in iTunes 8.2 (9.0 works too). Here are the instructions from my previous walkthrough, nothing has changed except the IPCC file you download.
 
Mac OS X:
Close iTunes if it is open
Start Terminal (Applications > Utilities)
Run the following command: defaults write com.apple.iTunes carrier-testing -bool TRUE
Windows 2000/XP/Vista (32-bit):
Go to Start -> Run (
type in "command" and hit enter
Type/copy+paste this into the command console that comes up: "C:\Program Files\iTunes\iTunes.exe" /setPrefInt carrier-testing 1
Hit enter
Windows XP/Vista (64-bit):
Go to Start -> Run (
type in "command" and hit enter
Type/copy+paste this into the command console that comes up: "C:\Program Files (x86)\iTunes\iTunes.exe" /setPrefInt carrier-testing 1
Hit enter
http://cdn.krillr.com/iphonetuts/3.1mms/ATT_US.ipcc
Download the modified bundle right (right-click and "Save as" or whatever your browser's equivalent is). To install this, follow these steps.
Download the file to some location on your computer
Plug in your iPhone
Start iTunes
Click on your iPhone in the device listing in iTunes
Alt-Click the "Update" button (Shift-click in Windows)
Browse to where you saved the IPCC you downloaded
Select this file and click Choose (or OK on windows i think)
Reboot your iPhone
You should now have working MMS! Unlike previous hacks, this one should not disable your Visual Voicemail feature. Feel free to email me if you have any questions or problems! :-)
 
Tethering tutorial will hopefully be available next week, once I figure out why previous methods aren't working ;-)