If your cell phone’s a globetrotter

If your trip is no more than two weeks long and you expect to rack up no more than about 50 minutes of calls, it will probably pay to use the phone with your current carrier. That is also by far the easiest option. Per-minute charges tend to be higher than with other options, but those require upfront investments that you might never recoup.

Before you go, inform the carrier that you're traveling abroad to ensure that international roaming is activated on your account and to ask about "world plans" that can reduce calling costs. With the AT&T World Traveler plan, for example, per-minute charges in the United Kingdom are 99 cents, compared with $1.29 without a plan. The plan costs $5.99 a month.

For tips on how to find other carriers' international calling rates and other charges, see the Before you go section of this article.

With a GSM phone you'll use a lot, consider switching the phone's SIM card. If you have a GSM phone you'll use abroad to make more than 50 minutes of calls, it's probably worth equipping the phone with a prepaid internal SIM card that will work in that country (it isn't an option with most CDMA phones). Though it's more trouble than continuing to use your own carrier's SIM, you'll probably save at least 50 cents a minute on calls, or at least $25 on overall cell-phone costs for your trip. Another benefit of using a foreign SIM card is that there's often no charge for incoming calls, even those calling from home.

Most phones sold by cell carriers are programmed, or locked, to prevent you from using the SIM cards of other carriers. It's legal for carriers to "lock" the phones that they cell into their network, but a 2006 ruling allows consumers to reprogram them. Most people are unaware of this. Even if they know, the process of unlocking a cell phone in the U.S. can be complicated and time consuming, and may result in compromised versatility.

You can unlock certain phones though (except for Verizon phones), and for some phones, the carrier can send you an unlock code. T-Mobile requires that you are a customer for 90 days to do this-unless you purchased an unlocked phone at the start of your contract. All AT&T says is that it will assist in certain circumstances. If you are planning to unlock your phone through the carrier, allow yourself some time, as it can take several days for the carrier to get the code to you.

With a little technical savvy, you can legally unlock a phone yourself with the assistance of some Web sites. Sites such as GSM Liberty, Unlock MyPhoneNow, and Uniquephones.com let you download unlocking kits for specific phones. Prices start around $10 for basic phones, and jump to $25 and up for smart phones like Blackberrys

Officially, iPhones cannot be unlocked, at least not by AT&T, but the iPhone is quad-band, so it's ready for travel. You still need to purchase the World Traveler plan to make less-expensive calls abroad, and you'll have to buy an additional international data package too, which runs $25 for only 20 megabytes of data. If you are so inclined, there are ways to unlock, but it's been reported that Apple has "poison pill" safeguards that will turn your iPhone into a "brick" if tampering is detected.

Another option—if you don't mind wading through endless discussion threads—is that you might be able to find out how to unlock your phone free of charge on such forums as Cell Phone Hacks. Another Web site, The Travel Insider, nicely integrates unlocking advice with hotlinks to services.

Also, beware of falling short of the 50-minute mark. Cards are usually loaded with 50 to 100 minutes of calling time, for $40 to $100, and those minutes typically expire within 90 days. That means you'll likely eat any unused time unless you plan to be back in the country soon.

Finally, you'll need to buy the cards, which you can order in advance of your trip from such companies as Go-Sim, Cellular Abroad, and Telestial. You might also buy cards in airports stores or local shops in foreign countries you're visiting, though confirm availability online before you go, because some countries will sell cards only to registered residents. You'll have multiple carriers to choose from, most likely with unfamiliar names. Price can help to drive your choice, of course, as can online coverage maps (one of our staff members was recently able to check coverage, down to the hamlet, before he left on a vacation to the remote Yorkshire Dales area of England).

For more tips on traveling internationally with your cell phone, see Survival tips for using cell phones internationally.