Just wanted to make a quick guide for those of you who upgraded to iPhone OS 3.0 but can't seem to be able to enable MMS and Internet Tethering. Please keep in mind that THIS IS ONLY FOR USERS ON AT&T. You might be able to use this on other carriers, but I highly doubt it. Step 1: You need to download a pre-released version of iTunes and the Carrier Setting. iTunes: http://d01.megashares.com/dl/897faff/itunes_8.2_prerelease_for_mac_os_x.dmg Carrier Setting: http://www.megaupload.com/?d=3IVMRD46 Step 2: You need to uninstall your current version of iTunes. Simply drag it into the trash then restart your computer. Step 3: Once you're booted up, install the special version of iTunes you just downloaded. You might get a warning that your library was created on a newer version of iTunes followed by iTunes quitting. That's OK, just go to: Home Folder>Music>iTunes and move your iTunes Library file to a safe location. Now try to relaunch iTunes and connect your iPhone. Go to the main settings of your iPhone and option + click on Update. Select the carrier file that you previously downloaded and wait for iTunes to finish. You will NOT get a confirmation message, so when it's done just disconnect and reboot your iPhone. Step 4: Once your iPhone has successfully rebooted go to: Settings>General>Network>Cellular Data Network Input the following information in the appropriate fields: APN: wap.cingular Username: email@example.com Password: CINGULAR1 MMSC: mmsc.cingular.com MMS Proxy: 188.8.131.52 MMS Max Message Size: [leave blank] MMS UA Prof URL: [leave blank] Now after that is done, you should be able to Tether and Send MMS. If not then I would suggest checking over the info above and ensuring everything is exactly the same. Step 5: Cleaning up Final step here. First quit iTunes and then drag it from your Applications folder into the trash. At this time, you might also want to return the iTunes Library file to its original position. You'll already have one there and you'll need to replace it with your original file. Reboot. Now after this simply download the newer version of iTunes on Apple.com and reinstall and you're done! All this info was gotten and compiled from previous threads. Some users struggle with MMS and Tethering while others don't.