I have a PDA phone and it's a mixed love and hate relationship with it:
The good parts:
1- The most important thing about it is the ease of making schedules and tasks on it
2- Easy to write notes and memorandums at a jippy
3- Almost able to connect with anything in the world: Infrared, Bluetooth, wi-fi, small USB, SD card readers.
4- omni powerful, you can install anything on your mind, for me: e-books related to physics, and other sciences
5- you can download scientific calculators and cash organizers and other very handy stuff
6- you can use a lot of toys like movie players, and full games (my field installed a full 1993 PC game on it), browsing the internet.
The bad parts:
1- very big
2- very heavy
3- very bulky in your pocket
4- stupid windows operating system is slow and unreliable
5- expensive
6- nowhere near as stylish as normal mobile phones nor easy to use
having said that, I have to admit, once you get used to the task managers and the schedule manager and the notes, you're absolutely hocked with it and you'll never be able to get rid of it no matter how much you try and convince your self about its drawbacks