If entering the MMS settings alone is not working, then you must find and edit the file named com.apple.mms_override.plist with a new code, this code worked for me, and fixed my MMS Settings for i-Phone 3gs T-Mobile. (You must be on a home network with WiFi)



Order of Steps to take:

1. Install OpenSSH, from Cydia on your i-Phone
2. Install WinSCP from your home computer
3. Use WinSCP to access your i-Phonce files (Wirelessly)
4. Locate com.apple.mms_override.plist (located in i-Phone) Location of this file is at /Private/var/mobile/library/references.
5. Open com.apple.mms_override.plist and replace the code.


The whole process is easy just follow the steps below to enable mms settings for i-Phone 3gs on T-mobile. This method is guaranteed to work

Install OpenSSH in your i-Phone, by following the easy steps:
 

1. GO TO CYDIA

2.  GO TO SEARCH

3. SEARCH "OpenSSH" and click on it.

4. CLICK INSTALL

5. CLICK ON CONFIRM

1. CLICK ON LINK TO INSTALL WINSCP, From your home computer.

http://sourceforge.net/projects/winscp/files/WinSCP/4.3.7/winscp437setup-sponsored.exe/download

2.  CLICK ON SAVE FILE

3. DOUBLE CLICK FILE

4. CLICK ON RUN

5. CLICK OK

6. CLICK ON NEXT

7.  CLICK NEXT

8.CLICK NEXT

9. CLICK NEXT

10. CLICK NEXT

11. CLICK INSTALL

12. CLICK ON FINISH.

Look up your i-Phone IP Address, From your i-Phone.

•  Go to Settings:

• Go to WI-FI

 

• Click on the blue arrow

• Look up your i-Phone IP address and save it.

Now, From your home computer.

1. OPEN WINSCP,

2. Enter your i-Phone IP address into Host Name
User name: root
Password: alpine
port number: 22

3. Press Login

4. Press Yes

4. Double click the back folder, to go back

5. Double click "mobile"

6. Double click " library"

7. Double click "Preferences"

8. Double click " com.apple.mms_override.plst

9: Replace old code with the following code:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>MMS</key>
<dict>
<key>GroupModeEnabled</key>
<false/>
<key>MMSC</key>
<string>http://mms.msg.eng.t-mobile.com/mms/wapenc</string>
<key>MaxMessageSize</key>
<integer>1048576</integer>
<key>MaxRecipients</key>
<integer>10</integer>
<key>MaxVideoBitrate</key>
<integer>131072</integer>
<key>Proxy</key>
<string>216.155.165.50:8080</string>
<key>UAProf</key>
<string>http://www.apple.com/mms/uaprof.rdf</string>
<key>UserAgent</key>
<string>SonyEricssonW800i/R1L</string>
</dict>
</dict>
</plist>

Click on Save

Reboot your iPhone, and now you should be able to send and receive multimedia files.


if the above method was too complicated or did not work, than please use the link below.

http://ifile-mms-tmobile-jailbreak.blogspot.com/