Is this a good way to get a new phone for Verizon?

I currently own a Droid 2 global by Motorola, and it is very "glichy" it freezes, locks itself, and shutdowns randomly. So a friend told me that I can take it to a Verizon store and trade it in for a new one, and if they don't have any droid 2's I get a phone of equal or less value. OR you can pay them the difference of $ from your phone from the phone you want, so if I trade it in because its bad, can I get the iPhone 4 if I pay the difference?