Unless you work for a company that reimburses mobile phone roaming expenses without too many questions—and how many of those are left these days—it is a huge gamble to keep your data service active when you travel abroad. Depending on how many services you have active, in addition to email, even mobile phones can chomp through massive amounts of data really quickly.

For the purpose of this column I just ran a quick check on my iPhone device with all my usual apps open: email, Twitter, an RSS feed reader and a couple of browser windows. My phone gulped down a little over 5 MB of data in 15 minutes without so much as burping. That is pretty steep at home, if you have data allowances, and it is suicidal abroad if you are roaming. What most of us end up doing, I assume, is switching off all data roaming when we travel. Only occasionally updating things when we get a Wi-Fi network to hop on to.

On the move: Download apps that you can use without going online.

You could carry a regular guidebook. Or write down everything you need before you leave your hotel. But where’s the fun in that? And besides, what do you do when something in your pre-planned schedule breaks down?

The trick is to find ways of using your phone offline. In other words, using apps, documents and maps that work even if your phone isn’t hooked up to a data service.

For instance, many of the Lonely Planet apps for the iPhone come with built-in maps that work offline. Keep your GPS switched on—which is free, of course—and the app will overlay your position on the Lonely Planet map. The map also displays the usual landmarks such as restaurants, museums and transport stations. Though there is a one-time payment associated with the app, it does save a lot of time by itself and in combination with a map or guidebook (you know where the restaurant is, but have no idea where you are yourself). There are offline maps available for the BlackBerry as well, and the TrekBuddy app seems popular.

The best way to think about this whole offline approach is to break it down into parts. You need something to help you with location, something that recommends places to go, see and eat, and something that helps you with travel.

What I usually do is to carry PDFs of Wikitravel guides and other free resources on my phone. The websites of most tourism development agencies all over the world will give you downloadable PDF copies of brochures. In most cases these documents give you quick, hassle-free recommendations. Now use something such as the Lonely Planet guide or some other offline map to help you with location. And finally I usually use an outstanding free app called MetrO to plan travel.

MetrO, I have no hesitation in saying, is the best travel app I have ever used. And the idea is pure and simple genius. MetrO helps you navigate through the public transportation network in dozens of cities all over the world. The cities range from Delhi—including the Airport Express—to Tashkent. The app is pre-loaded with route details, estimated transit times, nearby landmarks and even a list of popular tourist locations. If there are multiple options to get from A to B, MetrO will give you both the shortest route and the route with the least changes. And the interface is simplicity itself.

But two things make MetrO particularly awesome. The app works completely offline. Updates are released frequently and you can add them whenever a data service is within reach. This means you can use it in the air, under the ground or on a ship. Also, MetrO is available for a variety of platforms: iOS, BlackBerry, Windows Mobile and Symbian, and the developers say that an Android version is in development.

Don’t leave home without it. You can download MetrO at http://metro.nanika.net

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