Can you use an unlocked iPhone 5 for prepaid and contract?

I'm currently looking at my prepaid options and I decided I want to get either the iphone 4s or the iphone 5.

After doing some research, should I buy an unlocked iphone 4s/5 from the apple store and use it with a prepaid sim card?

Also, if I want to get a contract later down the road, can I still use the same iphone I bought and just use a sim card?

What kind of carrier are you gonna use?

I encountered a similar issue with tmobile. I had a prepaid plan and I wanted to use it for iphone 5. But when I went to my local dealer, he said if I wanted to get it I can't use it on a prepaid plan. Even though I thought you can use an unlocked phone in any contract, I imagine that tmobile won't allow you to use it on a prepaid plan. Why don't you ask your carrier?

Yes you can, first hacktivate it then use a mirco siim card cutter or cut it your self to fit in the iphone sim slot. I hacktivated correctly for my friend and hes currently using it for tmobile 50 dollar plan…