Upgrading to Iphone 5 in contract?

Hi, I'm still in contract with an iphone 3gs which end at the beginning of 2014. I would like to buy the iphone 5. Can I just buy an unlocked one from apple and use my 3gs sim in it? Will everything work the same? Also what are my other options?

Yes but its like 600. You can upgrade your sim for free just pay the shipping and handing or pick it up from the store. Because new phones have micro sim

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