GSM and CDMA UK/USA

[megabyte]

I live in England and will be moving to Virginia, USA. I am thinking of buying an iPhone that I can use on a pay-as-you-go sim card in both countries although I would want to have the option of GDSM if I change my mind. I do not want a 5 purely because of the price, so that leaves me with the 4S. Looking at this site: Identifying iPhone models it shows the iPhone 5 has one which covers both GSM & CDMA, but on the 4S the second model does not show which it has. It also shows the 4 has one or the other. Does anyone know?

Also, I would appreciate any info that I should be aware of so I do not make a costly mistake.

Thanks