I carry both the iPhone and the Crackberry, each has it's place and each has their strengths and weaknesses. I find the tactile keyboard of the Crackberry easier for typing and the iPhone has a better graphics display for watching movies and the latest You Tube Video.
With traveling my go to, must have application is TripIt! Once installed it monitors your e-mail account looking for your confirmation e-mail from hotels, airlines and rental car companies. Once it finds them it then organizes them inside TripIt as a separate itinerary for each trip. It gives you map of your hotel, touch the map and it opens up Google Maps and uses the iPhones GPS to get you there. If you travel with others you can create a group so everyone can see each others itinerary. You can also e-mail your itinerary to a loved one.
Now here's some really cool extra stuff that you get....it offers you seating advice, for example on a Boeing 737 rows 2-10 has and extra inch of legroom and rows 1-10 offer an extra degree of pitch in the seat.
It also lets you know of gate changes and delays...this afternoon our flight was delayed TripIt let me know a solid 5 minutes before the gate agent posted it.......5 minutes when your making a connection or trying to get home can be the difference in being able to switch flights or getting stuck for the delay...unfortunately today the 5 minute head start could get me on an earlier sold out flight.
Tripit offers a free and a paid version, the free version is all that I use but the paid version tracks all your hotel and mileage points. It's not worth the $50.00 yearly fee and the click through adds don't bother me.....I have it loaded on my wife's iPhone so see can always know where I'm at and hopefully what time I'll be back.