You can still bring in an unlocked, unbranded smartphone device (not all makes/models, but some) and avoid the mandatory data plan with both ATT & T-Mo. ATT still mostly looks for their own devices, along with iPhones & Nexus variants. Not even all the HTC models w/ ICS (etc.) get flagged, believe it or not. I didn't go into this much detail since the OP seems to be fixated on sticking with his big 'V' family plan.
I realize you used to work for them, but that's *still* currently the situation w/ ATT. Ask around if you don't think it's true. Merely placing your SIM card into a smartphone doesn't necessarily mean they will send you the dreaded 'upgrade to a data plan' message. Right now I can bring in quite a few handsets with no issues <pointing to the table full of various smartphones>. Obviously the OP's asking about Verizon, which is a different situation altogether.
FWIW, Plenty of folks are using unlocked iPhones with Prepaid too, FWIW. You just have to be willing to give up all the post-paid feature you would get otherwise. Even the MVNOs using ATT's network, such as H2O, make good places to keep a unsubsidized or hand-me-down smartphone on the line but w/o spending an extra $20-30 each month.