If i get an iphone 4s unlocked in the US will it work with vodafone in ireland?

Hi , my relatives are coming over from america for christmas and i was wondering if they got an iphone 4s unlocked over there would it work as a pay as you go over here on vodafone ? hopefully that made sense but this is my only way of getting an iphone :p

Thanks :)

Yes,I did the same...But unlocked phones are quite costlier so I bought a locked one and unlocked it using the permanent remote unlock service from Classicunlocking.com and removed the network lock and then I was able to use it with other GSM networks.