Using your cell phone on vacation in the U.S. or Canada is generally as simple as using it at home (though, if you're crossing the border, it's worth checking for plans that discount the cost of roaming).

Travel anywhere else, though, and things become more complicated. Foreign countries generally use only one of the two major cell-phone technologies used in Canada and the U.S. (See GSM vs. CDMA.) GSM is used in most areas of Europe, while CDMA is used in much of Asia and parts of Latin America. In the U.S., Verizon and Sprint Nextel use CDMA networks, while AT&T and T-Mobile use GSM.

If your phone doesn't match the country's network, you'll need to either rent or buy a "world phone," a GSM phone with the ability to interface with foreign and U.S. networks. Even if your phone uses the technology of the country you're visiting, you might need to contact your carrier before you leave to ensure you can use it abroad and to sign up for discount rate plans.

Failure to plan your mobile phone use before you leave can cause cell shock when you return and open your phone bill. With per-minute costs of between $1 and $2.50, even in less expensive regions like Western Europe, and $5 and up in pricier destinations like Eastern Europe, Africa, and Asia, it's all too easy to spend hundreds of dollars on cell-phone service, even on a relatively short trip.

Planning cell phone use abroad starts with these three tips.