Can purchase an unlocked iPhone in US and use it in Malta

Hi all

I'll be visiting NYC in the coming months and I would love to own an iPhone 4s! I am interested in buying an unlocked iPhone 4s from an authorised Apple store in NYC as the current prices in my country, Malta for an iPhone 4s is $800 with one of our service providers and its quite expensive :/.  Would I have any problems if I use my local SIM card on it in Malta?