"Travel apps are great, but watch out for roaming charges," I wrote in 2009. Five years on, little has changed. Data roaming remains too expensive for dawn-to-dusk app use in most countries. Fortunately, some apps work fine without an internet connection. So, even after you switch off mobile data for take-off, you aren't flying blind.
Some guide apps work entirely offline. Pre-loaded maps locate you using GPS, which uses no data, then find the restaurant, hotel or sight you require. Sometimes you need to use the map service on the app before you travel to make sure it is ready-downloaded, or cached. To check this has happened, test before you travel by switching on 'airplane' mode and trying to use it before you travel.
Travel 'utilities' often rely on a 3G or Wi-Fi connection, however. Google Translate and other translation apps are less powerful without internet, for example. Visual translator Word Lens (Android, iOS, Google Glass; free) is one language app that works perfectly offline. Point your smartphone camera at foreign words and an English translation appears on the screen. Word Lens can handle simple blocks of text, such as menus, newspaper headlines or road signs, in French, Spanish, German, Italian, Russian or Portuguese. In May, the app developer was bought by Google, so expect more integration with Google's vast translation capabilities soon.
Currency converter XE (xe.com/apps; Android, iOS, Windows Phone, BlackBerry, Firefox OS; free) uses data to calculate accurately at live mid-market rates. But the app also caches the last rates used, so works offline. Unless there's a market crash while you are off the internet, conversions will be fairly accurate.
Perhaps my most important travel utility is a map, but online services like Google Maps need a data connection to work fully. There are alternatives. For driving, CoPilot (copilotgps.com; Android, iOS, Windows Phone; free) works well if you are travelling to the US, UK and parts of Europe. You can install one country map from a long list for free, after which you expand your collection via in-app purchases. It costs extra to add satnav-style voice navigation. Windows Phone devices have offline navigation courtesy of the HERE app now available for Android; see here.com/download).
The Telegraph, London