ok i have mms and data working on ios6 settings on video are outdated there are no wap.cingular
here are the instructions to get mms and data working no
http://www.unlockit.co.nz needed
SystemConfiguration/preferences.plist
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replace phone to att.mvno you will find two "phone" in this .plist replace both to att.mvno
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Library/Preferences/com.apple.mms_override.plist
use this text:
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<?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://mmsc.cingular.com</string>
<key>MaxMessageSize</key>
<integer>1048576</integer>
<key>MaxRecipients</key>
<integer>10</integer>
<key>MaxVideoBitrate</key>
<integer>131072</integer>
<key>Proxy</key>
<string>66.209.11.33:80</string>
<key>UAProf</key>
<string>http://www.apple.com/mms/uaprof.rdf</string>
<key>UserAgent</key>
<string>SonyEricssonW800i/R1L</string>
</dict>
</dict>
</plist>
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6. Then click the checkmark on those two file and restore to the iphone using iBackupBot software
7. It should restore and after reboot MMS should start working.
Note that you may need to follow these instructions again if MMS stops working after an iOS update.