10/9/2015
My experience with installing and running CM12.1 on LS740 for Virgin Mobile...
All installs done using TWRP 2.8.6.0, with an advanced wipe (everything except external SD) before any reinstall of CM12.1
1. Installed CM12.1 "Updated 9-20-2015" build linked in the OP. No problems.
2. Installed the PA-Gapps Pico "5.1-20150329" build linked in the OP.
Keyboard breaks (crashes every time you request it, so you can't type or sign into the play store to update).
START OVER (advanced wipe)
1. Installed the "9-20-2015" CM12.1 for volt
2. Installed the PA Gapps build "pa_gapps-modular-pico-5.1-20150315-signed" from AFH.
Keyboard works.
3. Installed the APN fix linked in the OP. Connects to carrier, 4G LTE no problem.
MMS do not download in the stock messaging app.
4. Installed the "stock MMS fix"
here which is listed on the APN fix page, although it appears to have been made for CM11 and not CM12/12.1. Reboot.
Phone is permanently stuck looping the boot animation (until forcibly powered off by holding power button/removing battery.
START OVER (ugh)
So, I don't know if others have truly resolved the MMS issue (without getting around it by switching to Hangouts) but I have not, the stock MMS "fix" breaks both LG Volts I have tried this on.
-Luf