How could I flash a Sprint IPhone 4 over to a different carrier?

My mom has a sprint iphone that she doesn't use any more and I wanted to take it to a different carrier like cricket or something. Would i have to jailbreak it or unlock it to do this? If so, how would i do that? The phone is updated to IOS version 6.1. If it isn't possible would i be able to take it to flash over to revol? Thank you so much to anyone who can help me with this.

Watch the YouTube tutorial in the source link to flash it to Cricket.