Can Sprint iPhones be unlocked?

My aunt has an iPhone 5 and she is upgrading to a 5s. She said she would give me her iPhone and I would connect it to MetroPCS. Can I unlock a Sprint iPhone and connect to MetroPCS? If so how much would it cost to be done?

Neither Sprint nor Boost use sim cards so you don't need an unlock. You need to flash the phone. And no, you can't flash a Sprint iPhone to Boost.

Yes but you need to unlock your iPhone first. I would recommend:

http://www.iPhoneFactoryUnlockUSA.com

They unlock sprint iphones for $20.

All you need to do is give them the IMEI number in your iPhone. (Navigate to settings < general< about )