As the name suggests, GSM is the standard in much of the world. Today, there are over 1.7 billion GSM subscribers in 210 countries, comprising 77 percent of the total world cell phone market. It is used in all parts of Europe (where the system began), in Africa, Asia, Australia, and increasingly in North and South America. (Notable countries that do not use GSM are Japan and South Korea.) What this means for the international jet setter is that in theory you can take your beloved phone and phone number just about anywhere in the world--and then make and receive calls to or from anywhere in the world. But practical reality is a bit trickier than the theory, so let's break it down into real-life terms.
The World of SIMs
We're not talking about the world's most popular computer game, but about "Subscriber Information Modules." If you have one, you also have a GSM phone. GSM carriers use smaller-than-postage-stamp-sized plastic chips to store your phone number, information about your account, and other saved personal information (like your phone book). This is what allows you to use different phones on the same network (by moving the same SIM from one phone to another), or to use the same phone on different networks (by swapping SIMs with a single phone). For example, you could take your Pink RAZR, fly with it to London, rush into the first Virgin Megastore you see, and 10 minutes later and 10 pounds (the money kind) lighter be chatting with blokes all over the UK. All you did was replace the SIM in your phone with a new SIM that works on British networks. But hold onto your RAZR for a minute, there are a few caveats and considerations.