THIS IS LAYED OUT BETTER
1. First things first. Make a full backup of your iPhone in iTunes.
3. Launch iBackupBot and just hit OK to all of the messages that may pop up. It may take a while to load all the device information if you have multiple backups saved on your computer.
4. Once loaded you will want to find your most recent backup on the left had side and select it.
5. Next you will see a list of files show up in the righthand box. Scroll down until you see Library/Preferences/com.apple.mms_override.plist.
6. Double click on the mms override.plist and it will pop up a box to edit the file.
7. Download this com.apple.mms_override.plist and paste the contents into the box or manually write it out. It should looks similar to the picture below which is for T-Mobile. Simple Mobile’s will look a bit different. The MMSC string should be http://smpl.mms.msg.eng.t-mobile.com/mms/wapenc
8. Now put a checkmark in the box next to Library/Preferences/com.apple.mms_override.plist and then click on File at the top and select restore.
9. iBackupBot will restore this new edited file onto your iPhone.
10. I will make a video Tutorial soon.
I'm on T-Mobile with an Iphone 4, and while mine is jailbroken, I thought my Cellular Data settings might help you. It's not a promise but try and see. You may get lucky.
MMS Proxy: 22.214.171.124:8080
MMS Max Message Size: 1048576
MMS UA Prof URL: http://www.apple.com/mms/uaprof.rdf
Of course Power Off then On for settings to take affect.
I have an iPhone 4 factory unlocked for T-mobile and just recently changed my setting to these exact settings and it fixed the problem. Didn't have to go through all that back up stuff to get it fixed. Btw thanks!
I wouldn't get to upset if I were you. There is another solution u might like and it's 100% free too. If you really wanna text you're friends and call and all that other cool stuff plus more you should get something called viber. It's a free app that let's you call your friends for free and text free and my MMS is screwed up too(only with pics and vids) if i wanted to send them a picture I would send it to them via viber(I'm an unprofessional artist I send pics to my family and friends every pic I draw), and I'm not sure if I'm crazy or if it's true but I could've sworn my friend used it on his computer when I went to his house.. But I know for sure it works on iPad iPod tablet iPhone every device but I'm not sure bout computer plus I think you get to use the number from the cellphone but if they text you on viber you'd have to open up viber to see the messages instead of your SMS messenger. It's actually pretty cool, I would show you a pic but I don't know how to show the pic to you since I'm new to this site.
PS: if I type as if I'm texting(abbreviating everything) I'm sorry.