Palm Pilots are useful little beans of technology.

They're possibly the most popular personal organisers, as they have an extremely flexible OS and nifty handwriting recognition system.

http://www.palm.com/

Also by TRG, Handspring, Sony and other. Try looking at PalmOS.

CategoryPervasiveComputing

For "teenagers," there is [Cybiko] wireless, 900MHz peer-to-peer HandHeld. They're pretty nifty. You can talk to other people within a 300 foot radius. It vibrates too.