The number of travel-related applications for smartphones is downright staggering, and many of them can really help the travel process. But are you sure you’re not paying through the roof to use them?

Many travel apps are related to going abroad, whether it’s a Paris city guide or an interactive subway map. But guess what? If the program is Web-based and not a standalone, you may be charged for international roaming and data useage.

Some users have been charged hundreds of dollars because they forgot to turn off international data roaming, or their phone was automatically synchronizing new emails while they were abroad.

According to AT&T, just opening a large picture in an email or downloading a short YouTube video can cost up to $40.

Before you fly, check with your carrier about roaming costs. Some carriers will give you specific rate information for your destination so there are no surprises.

Others have international package that allow you to pre-pay a set amount.

But remember, a “roaming plan” often just applies to voice usage. Data roaming is a whole other package.

And no matter how “smart” it is, your phone shouldn’t be your only resource on the road.

After all, you don’t want your phone to conk out while you’re trying to find your location on Google Maps. Always keep a paper trail as a backup.

Get more technology advice in our Travel Gadgets & Gear section.

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