iMessage should work fine, location based reminders on the other hand are iPhone 4 and 4S only.

doesnt work for me..what do i do to make it work?? I cant see any option under messages for activating iMessage.

This makes me wonder how the majority of the people are even going to use it if it isn't immediately obvious how to activate it. I used this gigaom article to setup it up on my 3gs: http://gigaom.com/apple/ios-5-imessage/

It works pretty well and I can't wait for the mac version.

Do you happen to know about iPad/iPad2?