If you're thinking about heading abroad -- either for business or pleasure -- your mobile phone could turn out to be as useful as a pebble in your shoe.

Most countries in the world today rely on GSM networks and require the use of GSM-capable phones. Until recently, that ruled out the majority of U.S. mobile phones, since most U.S. wireless carriers only used technologies based on other cellular standards or protocols, such as CDMA or TDMA.

Things have improved, though. Several U.S. carriers also support GSM these days, to one extent or another. AT&T Mobility (formerly Cingular Wireless), T-Mobile USA, and some other U.S. wireless carriers now offer plans that'll let you use certain cell phone models in both the U.S. and other regions of the world.

Beyond these big carriers, dozens of Web-based start-ups have now sprung up with the specific aim of providing global mobile access. (We list some of them at the end of this article.) But when you look at all the choices in this burgeoning emerging business segment, you'll find a mare's nest that might seem daunting enough (at first) to make you want to ditch your travel plans and stay home.

To begin with, even if you have a GSM phone that works in the U.S., it's quite likely that this device won't function anywhere else. On top of that, even if your GSM phone performs quite well in Greece or Italy, you might not be able to use the same phone while traversing the mountains of Switzerland.

Pricing schemes can be just as confounding. On the device side, the options basically boil down to either buying or renting a GSM cell phone. You'll also need to contend with at least two other types of charges:

• Daily, weekly or monthly service charges for international calling plans.
• Fees per minute for individual calls placed by you (and sometimes to you).

Pricing in each of these categories can vary considerably from one provider to the next, often without much (if any) apparent rhyme or reason.

This can become very confusing, especially because what works in one country won't necessarily work in another. For example, suppose one of your colleagues had a great experience with his Haier D6000 cell phone rented through CellularAbroad on a recent vacation in Paris -- if you're traveling to Madrid, his advice won't do you much good, because the Haier D6000 doesn't work in Spain. Or Argentina, Jamaica, the Bahamas, or Switzerland.

In other words, before opening up your wallet, you need to take a close assessment of the services available as well as your own individual needs. If you start by asking yourself the following five questions, you'll be well on your way toward finding a solution.