Using Your Smartphone Overseas
I recently had to figure this out on my own while traveling to France and Turkey, so I hope this article saves you a wee bit of research. While traveling around the US very few of us ever think about the antenna, or radio system, on our smartphones. But unless your phone has a GSM band antenna it is probably not going to work overseas.
GSM which stands for global system for mobile communications, is the most popular mobile phone standard worldwide. According to PC Magazine, in the US currently AT&T and T-Mobile use the GSM band. Verizon, Sprint and US Cellular use the code division multiple access band or CDMA.
GSM carriers put customer information on a removable sim card. So if your GSM phone is unlocked, then you can purchase a sim card once you arrive overseas and place it in your phone. Until you get your new sim card keep your phone on airplane mode to avoid international charges.
What you are doing specifically when you buy a sim overseas is buying a daily or monthly plan on a local network in your overseas location and registering your phone on that network. This means however, that people won't be able to reach you at your regular phone number, but you will be able to use your phone to reach them if necessary and to search the net, send and receive email depending on what plan you buy.
If you are committed to keeping your CDMA phone, but want to stay connected while traveling then you may want to buy a basic unlocked gsm phone at a store or online in the US, that only calls and texts. Currently these cost $25 and up. You can even opt for a basic gsm android phone for between $100-200 if you want to access your favorite apps etc while traveling. Either way, once you do this then you can buy and register a local sim card in your overseas' destination airport or city and be ready to go.