I have made the switch from a Pearl to the iPhone. I forward all my work email and have it set up via IMAP through yahoo. So it works flawlessly with iPhone.
Also iPhone has Terminal(3rd party app) which is great since I can access my work server through SSH/UNIX.
I LOVE the touchscreen and infact prefer it to the blackberry keyboard. Its soo responsive and intuitive. It takes some getting used to but after 2 weeks you become a pro.
Now I don't need a phone + iPod + laptop(not as often, but still need it off course). Just one device. I can surf the internet on the train, listen to music, and check work email.