World roaming on your cell phone
When packing for an international trip, there are a few essentials that you should always take with you. Besides a passport, a power converter, and a translation dictionary, the near-ubiquity of cell phones makes them yet another item for your suitcase. Whether your travels are for business or pleasure, a cell phone can be a huge convenience when trekking around London, Lagos, or La Paz. You can keep in touch with clients, fellow travelers, or the folks back home; make hotel, dinner, or show reservations; send "wish you were here" camera phone photos; or simply keep the phone for emergencies. And besides, since you'd rarely leave home without your cell phone, why should you leave the country without it?

Before you head out for the airport, however, there are a few things you should know. Not all cell phones will work abroad, and not all carriers offer roaming in every country. Before you make or receive transborder calls, you'll need to find out if you can do it, where you can do it, and how much it will cost. In the pages that follow, we'll answer all those questions to help get you on your way.

Know your technology
The first step in understanding world phones is to know the difference between two main ingredients in the cell phone alphabet soup: GSM and CDMA (see our cell phone buying guide for more information). In short, GSM and CDMA are the main cell phone networks in use in the world today. GSM, or Global System for Mobile Communications, is the predominant global technology and is used in Europe (where it's the standard), Canada, Latin America, the Caribbean, Africa, Australia, and New Zealand, as well as much of Asia and the Middle East. In the United States, AT&T (formerly Cingular Wireless) and T-Mobile operate GSM networks.

CDMA, which stands for Code Division Multiple Access, has less worldwide coverage than GSM, so your choices will be more limited. One of its biggest markets is the United States, where it used by Verizon Wireless, Sprint, and a number of smaller carriers like Alltel and US Cellular.

Outside of the States, you can find CDMA networks in Canada, Mexico, New Zealand, China, Taiwan, South Korea, parts of the Caribbean and Latin America, and a handful of other countries. The United States also has a third network called iDEN, but it's exclusive to Nextel and is present in very few nations.

More cell phone resources from CNET