First of all, if you bring your own phone, you would not have to sign a contract. Where is this iPhone 4 from? If you are bringing it from another provider, it will most likely NOT work on Verizon's network. You would have to purchase a new phone.
The Iphone 4 is from verizon. The reson im asking is because my provider is Cleartalk and i wanted to flash it but they can't because of the new ios 7.1 update. They dont have it yet....in order for them to flash it, the phone has to have an iOS of 6.1.4 or below.