I need to know if I buy an iPhone 5 or 5c in the US whether it will work in the UK with a PAYG sim

Question

I am currently living in the USA but will be moving back to the UK next year. I am not familiar with US phones or network providers. I have done a little research re CDMA / GSM  / frequencies etc but am just confused!!!
I would like to buy my daughter an iPhone but would like her to be able to use it when we visit the UK on vacation or when we move back. Ideally I do not want to be tied to a contract here and would prefer PAYG but if thats not an option would possibly consider it.
Is this going to be possible?
If so What do I need to be looking out for?
In the UK it is quite simple...I would just buy an unlocked phone or have one of the UK carriers unlock it for me and then just use overseas with a PAYG sim but are the phones here sim free?
Please help.
Many thanks
Jo

Answer 1

The answer is complicated. None of the major carriers offer PAYG service in the US, but if you buy a contract-free phone for full price you can get a plan that can be canceled at any time from any of the major carriers (AT&T, Verizon, Sprint and T-Mobile). There are smaller resellers that offer PAYG service (StraightTalk, for example), but they are hard to deal with.
The most liberal is the GSM carrier T-Mobile. They have "unbundled" the phone from the service, so if you bring your own phone or pay full price for a phone the monthly cost will be lower.
The other 3 will charge you the same monthly cost whether you pay full price for the phone or get a subsidized phone.
Verizon iPhone 5 series phones are unlocked out of the box for international use (thanks to a condition the FCC imposed on Verizon when they were allowed to buy a substantial chunk of spectrum). They are the only phones sold in the US that will work on LTE bands in the UK and Europe.
Sprint is not a good choice, because they give you a hard time if you want to unlock your phone.
AT&T phones are locked, but they will unlock the phone if you pay full price or pay off your early termination fee. However, they will only work on GSM in the UK, not on LTE (4G).