The iPhone Carrier Spread in the U.S.
Apple launched its first CDMA iPhone to U.S. users in early 2011, when it made the iPhone 4 available on Verizon's cellular network. With the iPhone 4S, the company released one model using a dual-mode chipset to work on Sprint and Verizon's CDMA networks and AT&T's GSM network. That means the phone can roam in other countries on either kind of network. Ideally, it would also mean
Foreign SIMs (subscriber identity modules) could be loaded into the phone to pay local rates while traveling abroad in GSM countries. However, that’s not how it works with the iPhone 4S, which comes locked to a specific network. To use it abroad, you have two choices: buy an unlocked mode…