Should I buy a locked iPhone & unlock it later?

I'm looking on amazon for iphones and I was wondering if I should just buy an.unlocked one or just unlock one later.

New iPhones have the ability to be unlocked with the factory settings; so there's no need to buy a specialty phone. Check with your personal carrier on what steps to take to unlock. If memory serves, AT&T requires that you have (or have had) an account to unlock. You could also buy new at full price and they'll unlock as well. Keep in mind that these details could change. If you get a "regular" phone through Amazon, you might be able to unlock it through a friend's account.

Hi, you can check with the following service what providers are supported for unlocking iPhone 4s: http://www.fastgsm.com/en/apple/apple/iphone-4s/unlock/country-network
This service provides an official carrier authorized unlock, which is the safest method if unlocking an iPhone.
Buying a locked iPhone will be way less expensive for sure.