Setting up Straight Talk MMS on AT&T Locked iPhone 3g, 3gs, 4 IOS 3.1 and Up
The only drawback from using the Straight Talk SIM plan on AT&T locked iPhones is getting MMS setup. Because AT&T Locked iPhones do not give us access to the Cellular Data Network screen we need to get creative on setting up the MMS feature. This is especially the case on iPhones with later IOS Versions. If you've updated your IOS to 4.x or if you have an iPhone 4, then you will need to follow these instructions. If you rather not mess with this stuff or just aren't technically inclined, then think about getting an iPhone directly from Straight Talk
AT&T locked iPhone 4 users, this is going to be the only way to get MMS working on your phones.
1. The first thing to be aware of is that you MUST jailbreak your phone and have Cydia installed, there's simply no way around this. Visit this page to select your model and follow the appropriate Jailbreaking instructions. All of the Jailbreaking instructions will use the RedSn0w jailbreaking utility which will let you install Cydia and jailbreak your phone at the same time. I highly recommend that tool because it only takes a few clicks to perform the Jailbreak.
2. So you've jailbroken your phone, now what? It's time to go to Cydia and install the TetherMe application. If you don't know what Cydia is, it's basically an alternate App store. The app is NOT available via the standard Apple App store so don't bother looking. This app will bypass Apple's security that locks down the Cellular Data Network screen. This app will cost you $4.99. Unfortunately, I have NOT found a free solution for this, that is unless you have early 3.0 or 3.1 IOS on your phone.
3. If you've never bought an app from Cydia, the first thing you need to know is that you will need either a Google account or a Facebook account, you will also need either a Paypal account or an Amazon account to use Amazon Payments. Cydia will guide you through the purchasing and installation process. It's not as easy as purchasing using the Apple App store.
4. Now that you have Tether Me installed, it's time to set up your MMS. To do so, go to Settings and scroll to the bottom and select TetherMe. Select Cellular Data Network which is now available. Complete the MMS section with the following: APN att.mvno , MMSC http://mmsc.cingular.com and MMS Proxy 126.96.36.199. Before you get too excited, your phone may loose the MMS settings any time you reboot it. So you will need to re-enter these settings any time you restart the phone. I have only tested on an iPhone 3g so it may be different on other phones.
5. That's all there is to it! Your MMS should work straight away, no need to reboot. As mentioned above, on my iPhone 3g, the settings revert back to being blank any time the phone is rebooted. I have not found a way to get it to stick so it may be somewhat minor inconvenience that you will need to live with.