Many people feel uncomfortable leaving their smartphones behind when they go to the gym, much less travel to another country. But if you're not careful, using a smartphone abroad can get expensive.  

Instead of paying for data usage by the gigabyte as you do in the United States, you get charged by the megabyte when you're abroad. And with prices as high as $2 per megabyte, the bill for uploading a Facebook video from Rome's Trevi Fountain could end up costing as much as dinner for two.

Voice calls can be expensive, as well, ranging from 20 cents to $2 per minute, depending on your carrier and where you travel. Text messages? Anywhere from roughly 50 cents to more than $1 if you’re attaching images.

More on Using Your Phone Abroad

Not long ago, the favorite strategy of many savvy travelers was to buy separate phones for use overseas. "I had a business card with three different phone numbers," says Phil Feinman, the co-owner of Architectural Supplements, a small Connecticut company with operations overseas. One number led to Feinman's U.S. cell phone, and the others to his cell phones for Europe and China.

That approach still works, but it has been joined by new options. Feinman pays $10 a day for an international pass from AT&T while traveling and says the practice has made his life much simpler. The other major U.S. carriers offer similar international plans with daily or monthly fees.The fees generally are applied only on days when you use cellular data. "It's expensive," Feinman says, "but if you don't use it you don't pay."

Effective tactics are described below. No matter which method you choose, try to rely heavily on WiFi to keep your data charges in check. And before you leave home, check the settings for your mobile apps. Shutting off updates or restricting the apps to WiFi usage can help you avoid expensive surprises.

Money-Saving Options

Check out your carrier’s world plan. If your phone is compatible with your host country’s cellular networks and you expect to have good WiFi access, consider using one of your carrier’s world plan options. One advantage: You'll retain your normal phone number, making it easy for people to reach you. Just warn them that their phone calls may cost more than usual. 

Sprint and T-Mobile grant their customers free text and data privileges in dozens of international destinations, but only at 2G speeds. For faster service, you need to pay a daily or monthly fee. Similar options are offered by AT&T and Verizon

Slip a foreign SIM card into your phone. If you're willing to briefly accept a new phone number, you can consider buying a pre-paid SIM card and using it in place of the one in your phone. (First, make sure your phone can work on overseas networks.) The cards are available online, in airports, and at stores and kiosks in many cities and they can be refilled via mobile app.

If you're going to be moving from country to country in Europe or Asia, consider an international SIM card, which is slightly more expensive, but can be used in multiple locations.

The SIM card in your phone is often housed in a tray that can be accessed by inserting a pin or open paper clip into a small hole on the side of the unit. On some smartphones, you need to remove the back cover and the battery to reach the card.

But there's an important caveat. Your phone needs to be unlocked before you leave home. U.S. carriers typically restrict smartphones to their own networks, preventing consumers from switching to a rival service too easily.

If your cellular account is in good standing you can request that the phone be unlocked. But don't leave this until the last minute: The process can take a few days.

Buy a budget smartphone. If your phone isn't compatible with overseas networks, or you just don't want to bring it along, consider purchasing a low-cost smartphone in the country you’re visiting. Or buy one from a trusted retailer such as Amazon. You should be able to find a good deal, especially if you tailor your search to unlocked Android smartphones.

The international version of the Huawei P8 Lite on Amazon was recently selling for $155, for example. The phone performed very well in our Ratings and it comes with a dual-SIM tray, which means you can use a temporary SIM card from the country you’re visiting as well as a SIM card from your U.S. carrier.

Turn off data and go WiFi-only. If you can persuade your family and friends to use an app such as WhatsApp, Facebook Messenger, or Google Voice you can communicate for free by text, voice, and video.

The Facebook Messenger and WhatsApp mobile apps offer completely free voice calling by using Voice over Internet Protocol (VoIP) technology: Your calls will go across whatever internet connection your phone is on rather than using your plan's minutes. Just make sure you're on a WiFi connection, because data charges will apply if you're not.

Both Facebook Messenger and WhatsApp require both parties to use the same app; both are available for iOS and Android phones. (Facebook has introduced a new tool for locating wireless networks around the world. You can access Find WiFi through the mobile app's More menu. To use it, you'll have to give the app access to your location data, giving up a measure of privacy in exchange for the convenience.)

With the free Google Voice service, you get your own phone number and can make calls to the U.S. or Canada for rates as low as a penny per minute, as long as you have a Gmail account. If people ring you when you're online, you receive the call via the Gmail chat service. When you’re offline, the caller is instructed to leave a voicemail message, which then gets transcribed and sent to you in an e-mail.

Tips Before You Go

You have your plane tickets, you've arranged to get your phone unlocked or simply gotten family and friends to download WhatsApp. So you're ready to start your trip, right? First, take a few minutes to do the following.

Back up the data on your mobile phone. You can use an external drive or a cloud-based service to save data such as photos and text messages. The same advice applies to the data on your laptop and other devices you plan to bring along.

Check to make sure you'll have WiFi at your destination. If you're going to a resort or modern hotel, that's a no-brainer, but WiFi may be harder to find in more remote, less touristy areas. 

Don’t forget your charger and appropriate power adapters. Many mobile devices can be recharged via a USB port on a laptop, as well. A Google search for “electrical plugs around the world” will reveal a number of sources to help you determine which adapter you need.