Edit: I was ask to add some details as to wat the zips doing and wat I do. I edit the mms-config.xml in the stock Mms.apk/SecMms.apk to settings from verizon which work for metropcs, I also use an apns-conf.xml that I edited for metropcs. the zip will mount data and mount system, it will delete Mms.apk/SecMms.apk and Mms.odex/SecMms.odex, it will delete dalvik-cache for Mms.apk/SecMms.apk, it will delete the telephony.db file in /data/data/com.android.providers.telephony/databases/ which countains apns. it will replace Mms.apk/SecMms.apk with the one I edited for metropcs it also replaces the apns-conf.xml in /system/etc/ which countains the default apns for the one I edited for metropcs (on first boot the phone will create a new telephony.db with the default apns countained in this apns-conf.xml, that is why this fix lasts thru a datawipe/factory reset). The zip will also delete devicemanager.apk/sprintdevicemanager.apk/sprintdm.apk to remove the activation prompt every boot.For more details take a look at the updater-script.
I am not responsible for anything that happens
UPDATE: I have updated the 4.1.2tw zip mms now works while connected to wifi, you no longer need to turn off wifi
New zip can be found here http://forum.xda-developers.com/show....php?t=2766197