Unlocking the iPhone after the contract period

Only the carrier the phone is locked to can authorize unlocking, so contact your carrier to see if they offer unlocking and whether they charge a fee(some do).

if the carrier doesn't offer carrier unlock, are they're the only ones who can do if for your i-phone. or if i bring it back to the US, can one of their carriers do it? I'm in the military and am just wondering if i bought a phone that's going to be a paper weight next year.

Unless the authorized carrier will unlock it, you're out of luck. No other carrier can unlock the phone for you.