[Electronic M]

You know you can buy a smartphone unlocked from anywhere walk into a T-Mobile store and have them drop in a sim card and activate it right?

That's what I've done everytime I switched or broke a phone under warranty (the box stores even the ones with a maintenance team don't really fix phones)... Granted until recently it was Sprint before they got bought out.
The nice thing about unlocked is if your carrier starts trying to screw you over you can just cancel service, toss the sim card, walk into a different carrier's store, pop a different sim card in and be on a different carrier just like that.

It's also handy for vacationing in the middle of nowhere. My family has a place so far out in the boonies that sprint didn't have coverage so I'd get one month of month to month coverage on another carrier that worked there, swap that sim card in while there and bounce back once I returned to an area of coverage of my main network...It worked great.