Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.
I just downloaded the new Microsoft Office Communicator Mobile client for my PocketPC Phone (I've got the Treo 700w). I must say - Communicator is simply amazing. I love the fact that I can use a consistent client application on my phone, at a kiosk, or on my PC.
So now, in addition to using my phone to get my hotmail, corporate email, browse the web, and open Word/Excel/PowerPoint docs, I can now search for anyone in the entire Global Address List and see their online status, IM them, send them an email, or call them (at work or on their mobile device). Great stuff!
Oh...and it's free to anyone who is licensed for Microsoft Office Live Communications Server 2005 with SP1.