I recently broke my iPhone 4s and am not due for an update for another year. My friend is going to let me use her old iPhone 4s. How do I deactivate my broken phone so that my friends phone will now be usable as mine? My carrier is Verizon
You can call Verizon customer support @ 1 (800) 922-0204. They should be able to deactivate your phone and activate the replacement. Even in the case of newer phones that are unlocked like the iPhone 6 - you still need a Verizon rep to activate the device after placing the SIM in it due to how their network is configured.
I simply put the old sim card into the "new" phone to immediately have phone access. I plan to call ATT and have the new phone officially activated.
Try to put your device in DFU mode then do a full iTunes restore. If not fixed then vist the apple store or call Verizon Support.