I can only confirm it is relatively easy with the leaked global ruu 4.03.605.2
IF you only really want voice and some random phone number, then you can just use your stock ROM that you already have.. I tested this, it works, I could recieve text messages and make phone calls (and receive phone calls). I dont think I was able to send SMS though, not sure.
Either way, just buy the SIM card, and put it in the phone.. power it back on, you get a warning about illegal SIM on the lock screen but everything behaves normally otherwise.
Thanks for the replies and help, figured I would post my findings, it may help others. I am completely bone stock. I bought a prepaid T-Mobile SIM and inserted it into Rezound. I went into the app LTE On/off and switched to "GSM/WCDMA,CDMA,and EVDO(PRL)" I immediately got bars once I did that. I was then able to place and receive calls. I could receive texts but not send. One thing to note is when I would go into Settings-Mobile network I would immediately lose the signal. I went into LTE On/Off and found it was back to its default Verizon setting. (it did this every time I went into Mobile Networks) Once I switched it back I got bars again. I think in the future before I put a different SIM in im going to just shut off the mobile networks.