i have a tmobile sidekick 3.
it has:
IM (aim, yim, and msn)
email
text messaging
address book
internet
calendar
notepad
to-do list
camera
mp3 player (mini sd card)
many programs that can be bought like calorie counters, sound recorders, and a plethora of games
in addition to being a darn good phone.
i have all my email addresses route to my phone, so i always know when i get an email, and the internet has saved me more than a few times... it's really great when i get lost. i can load up mapquest on it and find my way out of lostness. and it's great when my real internet goes down *grumbles*.
the camera is useful if i'm not carrying my real camera (which i carry 99.9% of the time) and i reallyreallyreally need to take a picture of something. aand... a lot of the features i never really use. i keep a paper notebook and a paper calendar-book thing, and i have an ipod... but i still love my phone. it has way more features, is way cooler, and way cheaper than the iphone. it's also from tmobile, which is way better (in my experience) than at&t, and one of my most favoritest things about it is the keyboard. i lovelovelove the keyboard.