Where did you buy them? if it is from Apple store, currys, phones4u or carphone warehouse it should be unlocked! but if it is a contract with Vodaphone, Orange/T-Mobile/EE, O2, 3 Mobile, Virgin etc. then it is locked to network. Before travelling ensure that you request to your provider to have it unlocked if your lucky, they will unlock it for you for free if not they may charge you, depends which provider you have. I had an iPad2 locked to 3 mobile but they unlocked it after a week for free, also I have an iPhone 5 from Vodaphone and they unlocked it within 3 weeks after I bought it for free!
Where did you buy them? if it is from Apple store, currys, phones4u or carphone warehouse it should be unlocked! but if it is a contract with Vodaphone, Orange/T-Mobile/EE, O2, 3 Mobile, Virgin etc. then it is locked to network. Before travelling ensure that you request to your provider to have it unlocked if your lucky, they will unlock it for you for free if not they may charge you, depends which provider you have. I had an iPad2 locked to 3 mobile but they unlocked it after a week for free, also I have an iPhone 5 from Vodaphone and they unlocked it within 3 weeks after I bought it for free!