Unlock Verizon iPhone 4 for free?

My aunt is wanting to give me her old iPhone 4, but the carrier is Verizon and I have Sprint. If I were to go to the Verizon store, could they unlock it for me? Or can this not happen? Or is there something I can use on the computer to do so (without jailbreak, surveys, and paying)? If you could please help, and not be negative, and explain in depth that would be helpful. Thanks!

Added (1). My aunt has Verizon not sprint…

Sorry, but your aunt's Sprint iPhone is not compatible with the Verizon network.