Will a US bought iPhone work in the UK?

Question

My dads going to the US for a few days and he said he would get an iPhone 5.
When he comes back to the UK will he able to use it here of he gets an unlocked phone from apple?
He will also be going to Saudi Arabia to live there so can be use it there?
I know that's a lot but if he can what carriers in the UK will he be able to use. He might be pay as you go. Thanks.

Answer 1

LTE is the latest version of high speed cellular data networks, 3G being older technology that is being replaced with LTE (LTE is a 4th generation technology).  Even if you do not have an LTE network in your coverage area yet, you should still get cellular data with any 4g/LTE capable phone or tablet, just your data speeds will be lower as you will have to connect with 3G or even something older and slower in some places.
LTE operates on many different frequencies, and different carriers in different countries lease different frequencies (depending on what is available to them and what they can get).  So if you buy an iPhone that does not support the LTE frequencies in use by the carriers in your area, you cannot get the benefits of LTE data speeds when using cellular data (and LTE is noticeably MUCH faster than 3G, at least in my experience with AT&T in the USA).
That is the pitfall of buying a USA phone and trying to use it somewhere else - you may find you simply cannot actually take advantage of the best service available to you (and no carrier discounts your data plan just because you naively bought a phone that does not connect to their higher speed network).