So if you bring your MVNO SIM card to activate your reserved Verizon iPhone on Selectel, would that satisfy them?
50/50 to be honest. You are technically "activating" the phone. I honestly think it will come down to the genius you get and the store. Some are very easy going about these things and others are sticklers (verizon SIM verizon phone, etc).
Especially in the case of the ATT iPhone, which may technically be locked even if paid in full until you call ATT. They can be ass hats with unlocking their phones.