Traveling overseas soon? I’ve got a warning for you about your phone that could save you big bucks.

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You can get hurt to the tune of hundreds or thousands of dollars in charges just by using your U.S. cell phone overseas.

The worst call I ever got about this was when someone went to Costa Rica and got a $30,000 bill for three days worth of calls. Another person I spoke with got a $6,000 bill for 40 minutes of use in a Canadian airport during a plane change.

They obviously didn’t have an international calling plan — nor were they with one of a handful of preferred providers who don’t rip you off when you use your phone overseas.

These carriers are exceptions to the overseas ripoff rule

There are three wireless carriers that give you a great deal when it comes to using your U.S. cell phone overseas.

The first two exceptions to the overseas ripoff rule are T-Mobile and Sprint. Both include with their plans the use of their phones outside the U.S. That means in most countries you pay nothing for texting, nothing for unlimited data and about only 20 cents per calling minute.

The third exception you need to know about is Project Fi. If you travel overseas frequently, you should become familiar with this little known cell phone service from Google.

With Project Fi, Google allows you to use your cell phone around the world at the same exact cost you would pay using it in the United States. If you have high-speed data here, you get all the high-speed data overseas. Ditto for calling and texting, which you get both here when calling around the United States and abroad when calling back to the U.S.

One notable exception, however, is if you call country-to-country overseas — not back to the United States. In that case, you’ll pay 20 cents a minute with Project Fi.

What if you’re on AT&T or Verizon?

The truth is, it’s terrible when you use either AT&T or Verizon overseas. They either charge you a massive amount if you don’t sign up for an international plan or they charge you huge additional fees to have an international plan while you’re out of the country!

That’s why I tell people that if you travel overseas a lot, you should really think about switching your cell phone service to T-Mobile, Sprint or Project Fi.

If you don’t want to leave AT&T or Verizon, the best thing you can do is buy a local SIM card for local service when you get where you’re going. For about $15 or $20, you can usually find one that will give you more than enough data for a month.

Lycamobile.com is the largest SIM discounter, with service now in 17 countries across Europe. In France, the cheapest provider is Free Mobile. Three.com is another big discounter that is now in eight countries.

All of these companies provide cheap calling both in-country and to the United States, as well as free or cheap texting and generous amounts of data.

Make international calls for free with these apps

The great news is that most people can avoid charges altogether by using a calling app like WhatsApp, Viber or any of a number of others that allow you to make calls for free.

One in particular you should know about is called Line. With Line, you’re allowed to make up to five free five-minute calls a day back to the U.S. after you watch a short 20-second video ad. You can even call somebody who doesn’t have the Line app on their phone.

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