I have a sprint iphone if I get them to unlock it does it void the waranty from apple also lets say I shut down my plan will it still work with the sim card?
Unlocking the iphone from the carrier is perfectly legal. It is simply a process to go from sprint-network restricted iphone to an all-networks unloked iphone. Just like the one Apple is selling for $650. Don't worry if it was not legal, Apple would have shut them down after a day doing that...
Regarding u shutting down ur plan, i am not sure i understand, if u shut down ur plan then u close down ur phone line, then ur sim is useless. Ur phone will still work but u will have no phone number to make or receive calls...