What is GSM and what is good about it?

The GSM family of networks, or Global System for Mobile Communications, is the most popular standard for wireless technology in the world with 3 billion users (41 percent of the population). 3G Americas , an industry group, reports an 86 per cent market share worldwide which translates into important advantages: callers get international “global” roaming so they can use their same phone number and device while traveling anywhere in the world—220 countries support GSM international roaming.  Because of this large market, there are more cell phone options from which to choose.  Roughly half of the phones in the United States uses the GSM family of networks including AT&T and T-Mobile.  The other half uses a different family of networks called CDMA.