OK I got my LG C900 AT&T working with MMS here in New Zealand after much painstaking investigation. Here's what I did:
1. Unlock the MFG app and log in to it. (probably best to dev unlock and prevent relock here while you are at it). Details here: http://forum.xda-developers.com/show....php?t=1021636
2. Make sure you are updated to Nodo update to have the latest carrier network provider files. T-mobile users must do this otherwise the files wont be there.
3. In MFG App, Enable ADC in the "engineer menu" under "other settings"
4. go to "set network profiles", if there are no network profiles in the box on the lower half of the page then observe the 2 boxes just above it, one is called MCC and one is called MNC.
5. You need to type in the correct numbers for your provider in these boxes. I de-compiled a flash rom and found out what these all are, you can also find out what they all are by browsing the windows directory of your phone and look for the provider XML files. In the file name of the XML file for your provider should be 2 numbers like this:
This is a T-Mobile US network provider file. The 2 numbers are MCC: 310 and MNC: 800
There may be mulitple config files for each carrier like the T-mobile guys have a lot of XML files and I dont know which is right for each of you so you will just have to try them one by one until you find what works. T-Mobile US is always MCC: 310 but MNC is different for different areas/states I guess. Here are the numbers for T-mobile:
MCC: 310 MNC: 160
MCC: 310 MNC: 200
MCC: 310 MNC: 210
MCC: 310 MNC: 220
MCC: 310 MNC: 230
MCC: 310 MNC: 240
MCC: 310 MNC: 250
MCC: 310 MNC: 260
MCC: 310 MNC: 270
MCC: 310 MNC: 300
MCC: 310 MNC: 310
MCC: 310 MNC: 490
MCC: 310 MNC: 530
MCC: 310 MNC: 580
MCC: 310 MNC: 590
MCC: 310 MNC: 640
MCC: 310 MNC: 660
MCC: 310 MNC: 800
So after you put in the two numbers, hit find and in the below box a provider config file will come up. Select it and your phone will now switch profiles and your MMS should now work, assuming you have the right provider config file. If you need help finding the right numbers for your provider, I may be able to find them for you.
I have no idea if this works on non-LG phones using the MFG app.
Hope this helps some people get MMS working