I searched google for a little bit and couldn't find any ICQ or chat clients that mentioned the V400. Most mentioned asking your provider what, if any, programs their service works with though.
I use to have a SideKick. Thing was a total POS. Had to return it for repairs 3 times in the first 4 months. I wouldn't mind having the BlackBerry 7230, the small version with the color screen. I've heard nothing but good things from people who own it ( or any BlackBerry model ). Just don't want to pay $300 for a phone.