Miley Cyrus

Buying an unlocked iPhone 4s and using it in the UK and America?

I am in desperate need of a new phone. I’m thinking about buying an unlocked iPhone 4s outright in the UK and then putting a pay as you go sim in it. however Im going to america in September for a year. would i be able to use that iPhone (unlocked) in the states? and do the states offer a pay as you go system that i could put in my iPhone if it did work there?

thanks for any responses! the other answers seemed outdated