You want to use your smartphone while traveling abroad. But choosing an affordable method can seem mind-numbingly complicated. Should you buy an international roaming plan? And if you do, what does 100 megabytes of data get you anyway? Perhaps you need a hot spot pass? Or a SIM card? If you don't want an eye-popping phone bill, it's essential to decide before you're on the plane.

"The pain you can get from just a couple of mistakes can be big," said Bill Menezes, a principal research analyst covering mobile services for the technology research firm Gartner.

With a little planning, however, you can stay in touch and on budget. Let's walk through the three simplest ways to do just that, from the most obvious to more creative (and cheaper) solutions.

Phone company plans

Major domestic phone carriers offer prepaid voice and data packages designed for foreign travel that you can buy before you fly, the option many people feel most comfortable choosing. The cost of a text message or the cost per minute of a phone call is fairly straightforward (check your phone company's website for pricing). But the cost of data -- sending text-only emails, posting photos on Facebook, checking into Foursquare, searching the Web for the addresses of restaurants and monuments -- is not.

Srini Devadas, a computer science professor at MIT, said sending emails doesn't eat a lot of data, but the fun stuff does. "It's the photos and videos and the maps," he said, explaining that emailing a single high-resolution photo is 2 to 5 megabytes. He estimated that a 10-minute video call would be about 24 megabytes.

Companies including Verizon and AT&T have megabyte calculators on their websites that let you estimate how much data you'll need by selecting the things you plan to do (send emails, upload photos, surf the Web) and for how long.

None of this is a science. How much data you use depends on a variety of things, including the resolution and size of your photos and videos. Always opt for the lowest when sending or uploading. Another way to save: When walking around a city, use offline mapping apps such as City Maps 2Go and OsmAnd, which can work without an Internet connection. (Such apps can take a toll on your phone's battery life, so consider the time-honored tradition of carrying a paper map.) And, of course patience will save you money: Spend the day taking all the photos and videos you want, but upload them later using Wi-Fi at your hotel.

Bottom line: Phone company plans are not always the most affordable way to go, but they offer one-stop shopping directly with your carrier.

SIM cards

Travelers who want to make local calls at their destination sometimes buy a SIM card (a microchip that can be inserted into a cellphone) from a provider other than their home phone company, which gives them a local phone number -- and local calling rates. To do so, your phone must be "unlocked," allowing it to be used on another network. Ask your phone company if it will unlock your phone (it might not) or search online for a phone that's already unlocked (Amazon's cell phones and accessories department has an "unlocked phones" category where you can find a used one for less than $50).

At your destination you'll need to visit a newsstand or mobile phone store to buy the SIM card (American suppliers generally charge much more), then activate the card with instructions that are, alas, sometimes in another language.

You won't be using your own phone number if you go this route. And because you'll have a local number, if anyone in the United States calls you and doesn't have an international calling plan, they'll get socked with a fat bill. (Check with your provider about SIM cards and calling plans, as there are special rates for some places, including Mexico.)

Bottom line: If you're an inexperienced traveler or, as Mr. Menezes pointed out, visiting someplace where you don't speak the language, there can be a learning curve involved in using a SIM card that you may not want to tackle. But this continues to be one of the best ways to make cheap local calls.

Hot spots

If you use a lot of data and want to avoid overage fees, your best bet is to turn off data roaming and buy an unlimited pass for citywide Wi-Fi instead. One company, Boingo, offers one-month unlimited mobile Wi-Fi access for two devices at more than 700,000 hot spots worldwide for $7.95. This is a recurring subscription, so if you want the service for only a month, you have to cancel, but there's no fee for doing so. You can see city maps with hot spots at Boingo.com.

Wi-Fi opens up a whole new set of affordable uses for your phone, like making voice calls and texting. Download Skype before you travel and you can make free phone calls (as long as both parties are members). You can text free too, using apps like WhatsApp. Note, though, that calls and messages through these services are free only if you're using them over free Wi-Fi. Data charges apply when you're not.

In some cities, you don't even have to buy a Wi-Fi pass, thanks to free public networks. Paris, for instance, has more than 250 free hot spots. Apps like Free Wi-Fi Finder, which works even if you shut off data roaming, can help you locate Wi-Fi.

Alas, free public Wi-Fi has a significant downside: Users are at risk of "sniffer" attacks, designed to steal information like IDs and passwords. Mr. Devadas advised against using Internet browsers to log onto websites like Gmail, Yahoo and Facebook. You would be wise not to do your banking either. It's less dangerous to download email through inboxes you configured in your phone's operating system. But of course the safest option -- and neither you nor I want to hear it -- is to avoid free hot spots altogether.

Bottom line: If you use a lot of data and are willing to gamble with free public Wi-Fi, you'll save serious money.

As you can see, each method has its pros and cons. Just be sure to choose before you travel. And remember: You're exploring someplace new. Soak it up. Put down the phone.