Nab a hotel room at the last minute Orbitz's mobile service lists hotels in 20 U.S. cities that have vacancies for that very night. You can't book through a PDA, however. Instead, Orbitz lists its phone number, which you can call by pressing one button. Be aware that Orbitz is known to charge more than if you call the hotel directly, so it's also worth contacting the property. mobile.orbitz.com.
Get directions and more The downloadable application of Google Maps is nearly identical to the version you've already used on a desktop. You can search for an address or just the name of a road, town, or business and then view the location as a map or a satellite image. The point-to-point directions, doled out one turn at a time on a PDA screen, are easy to follow, and there's even a feature that reveals real-time traffic info. google.com/gmm, free.
Scope the scene at the airport Using FlightStats, type the three-letter code of the airport you're flying from or the beginning of the airport name. You'll get an instant response with an estimate of how long the airport's security line will be, based on data from the Transportation Security Administration. The service also tracks delays for airports and specific flights. mobile.flightstats.com, free.
Learn about changes in your itinerary Anyone who has booked a flight, package, or hotel through Orbitz can sign up to receive free instant alerts on a PDA about delays, cancellations, or other involuntary changes (mobile.orbitz.com). Many airlines have a similar alert service for flights.
Translate languages Beiks is the leader in foreign-language tools for mobile devices, selling downloadable dictionaries and phrase books for 26 languages. Some of the programs from Beiks will even pronounce words and phrases for you. beiks.com, from $8.
Check the weather forecast There are dozens of ways to get weather reports with a PDA, but the Weather Channel's service is the quickest and easiest. It gives extended forecasts for 98,000 locations around the globe and pulls up storm systems on radar maps that look as good as they would on a computer or the TV news. www.weather.com/mobile, free.
Find the perfect restaurant Zagat to Go contains the same restaurant, hotel, and nightlife reviews as those offered in its books and subscription-based online service. With one download, you get the scoop on where to eat, sleep, and hang out in 77 cities--including 41 in the U.S. Sign up for the the free two-week trial just before you head off on a vacation; that might be all you need. zagat.com, $30 per year.
Figure out what time it is--anywhere Of the many world-clock programs available for download, perhaps the best is the PalmaryClock. Available only for Palm Treo devices, it lets you point to any location on a map and instantly get the local time. A shaded area on the map shows where it's currently nighttime. palmarysoft.com, $15.
Transform from PDA to GPS To get the GPS capability on your PDA to work, you have to pay for a service such as Teleav. The monthly fee may very well be worth it. A satellite pinpoints your location, and when you plug in the address of where you want to go, turn-by-turn directions come from the PDA's speaker. Directions are available for drivers and walkers. The Biz Finder feature steers you to gas stations--it'll even search for the cheapest option, if you like--as well as to restaurants, hotels, and attractions. telenav.com, from $10 per month.
Unless noted, all of these services will work on PDAs with standard operating systems such as Palm OS or Windows Mobile. Bear in mind that you may need a few free megabytes of memory to download any of the applications.