I was using Straight Talk service since the iPhone 4, then I switch to the iPhone 5 and works very softly and special the cost is the best $45 for unlimited data, text and calls, than other prepaid services in USA. The coverage is the same that at&t network and has 4G LTE service in the most important metropolitan areas.
Since today Straight Talk though the Walmart Stores is offering the iPhone 5 unsubsidized for $649 (we guess this is a CDMA (Verizon carrier model) but the option to use the GSM Nano Sim Card overseas. On the Walmart website they are listing several models of iPhone 5 of 32GB and 64GB capacity, in the description list GSM model A1428 and CDMA model A1429 unlocked as the Apple website states.
This is not the first mobile virtual network operator (MVNO) that offers the iPhone, Virgin Mobile and Crickett offer CDMA iPhone 4 the last year, but this is the iPhone 5 that was released in the last October, and is very hot smartphone.
The other plus is that you have Walmart Credit Card or apply for it, you can finance the cost of iPhone 5 for 26 months without interests (this is a payment of $25 monthly), this is limited offer until April 30, 2013.
I suppose that the iPhones are unlocked to use overseas, because if they are only CDMA will not work with the american GSM providers that have a different band frequency signal. But in Europe and Latinamerican regions will be easy to use replacing the SIM card of any carrier.