This wont work for everyone and sorry for the wall of text, but the following worked for me (calling and sms/mms after lte borked):
tldr: Play dumb on phone to vm/boost, get your msl, disable ehrpd and lte and run with 3g evdo rev A for now (yes thats what i said)
I only use my phone for calling and texting, only data i use is wifi based. I switched to an lg tribute after a bad flash and losing lte and having a flaky signal that cuts out every few minutes with ehrpd, and while its a nice phone its not a volt lol.
I tried everything to fix my volt, and i mean everything, even swapped out a known working uicc/sim from the tribute (yes i know, blah blah locked blah blah wont work, but im using the sim i got from the tribute in my volt right now after choosing to activate the meid from the volt with the tribute sim. Ehrpd 3g worked just like the volts sim did.) I ended up wiping out my carrier partition and messing with advanced data menus (which only screwed more things up) and still couldnt fix the flaky radio and no lte problem, so i decided to call vm and play dumb to get my spc to access even more advanced data menus.
Call virgin or boost, play along with them when they tell you to ##72786# and other stuff, after each thing they tell you to do, tell them that the phone is asking for a six digit code, and if they hesitate to give you your msl kind of dumbly say "oh, i guess its asking for something called an spc?" Thats what did the trick for me.
Once i got my msl, i went into the ##data# menu and disabled ehrpd and lte, and now 3g evdo rev A works great and i can finally call text and send and recieve picture messages again. 3g data seemed to work, i could access virginmobileusa.com no problem. At least my volt can be used now until we figure out a real solution to the problem.
Like i said, its not going to work for everyone, especially those who pay for data and want lte, but it might help a few of you. Its definitely something with the phone itself, either there is some setting i overlooked or my sim is fried after that bad flash, but the same symptoms arise with a new known working sim/uicc so it has to be firmware (on phone) based.