Unlocked iPhone 5 from the US works in Ireland?

I'm going to Chicago in a few weeks and I realised how much cheaper it is to buy an iPhone over there than in here in Ireland. I know you can buy them unlocked so I was wondering if I could bring it back to Ireland and it would work on Irish networks, like 3 or O2. Any help would be appreciated!

Maybe

Check the safe and easy unlock guide:

http://iphonejailbreak-unlock.com/how-to-unlock-jailbreak

You can use an unlocked phone anywhere… They are really expensive though

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