It's a good thing that every smartphone out in the market has a solution for travel and I have been using some applications that have helped a lot. I currently use 3 phones: iPhone 4, BlackBerry Curve 8900 and a Nokia N8. But I'll just focus on apps available for iOS and BlackBerry. There was a time where the Symbian platform had great travel apps, but as developers have moved away from that, the quality of apps available has gone down. Some of the iOS apps mentioned are also available for Android and even on BlackBerry.
- TripIt - my essential travel app. I can't make a decent itinerary without it. Upgrade to TripIt Pro is worth it if you travel a lot within the United States. (iOS, Android, BlackBerry)
- Hipmunk - a great travel search and booking engine where it takes into consideration the potential stress and time between layovers. Shows results in a timeline so you can compare price and flight times. (iOS, Android)
- Skyscanner - similar to Hipmunk but with a wider airline availability. It provides some pretty weird results. Tried to find flights from Manila to Jakarta and it gave me a suggestion to take a flight with Qatar Airwarys with a layover in Qatar. I'm not booking that flight for sure. It has a local site though that provides pricing in Philippine Pesos. (iOS, Android)
- XE Currency - No doubt the best currency calculator site out there. (iOS, Android, BlackBerry)
- TripAdvisor - great site when checking out hotels and nearby places of interest. I get a kick out of the user posted photos of bad hotels and weird stuff being discovered. (iOS, Android)
- BlackBerry Travel - I used to have TripIt and a bunch of other travel apps in my BlackBerry but when BlackBerry Travel came out, I decided to just use it exclusively. This is actually a rebranded WorldMate that takes advantage of the BlackBerry's mobile functionality and executes flawlessly.
I would give TripIt second place since it is multi platform and very flexible. I can write my whole trip itinerary with this service. Upgrading to TripIt Pro is an option and seems to be more useful for frequent flyers in the United States rather than world travelers.
There are many apps out there that try to solve some particular travel issues, but the list above provides me all the functions I need whenever I'm out of the country. Happy travels!