OK, first let's get the naming clear. Microsoft seems to be using 3 different names for this service as of right now: "Hotmail for Windows Mobile," "Windows Live Hotmail for Windows Mobile," and finally "Windows Live for Windows Mobile." I am yet to find out which name has been used for the most recent publishing of the application, but I would go with "Windows Live for Windows Mobile" because of the "About" screen for the actual application.
The application (which includes Hotmail and Spaces features, but not Messenger) has been available since June of this year, but until recently have I begun to notice links to it across Windows sites. In my case, I spotted it on the Windows Mobile "Total Access" site and here's the link story.
First noticed it on the "Download for Windows Mobile" page on the "Total Access" site.
So that takes us to "Windows Live Hotmail for Windows Mobile" page (already we note a name difference).
After downloading and installing it, we get the "About" screen, which might point us to Microsoft's real naming of the application as "Windows Live for Windows Mobile."
I'm currently going to test it out on my Windows Mobile 6.0 (6.1 is going to be available to us soon, yay!) powered AT&T Tilt and I will get back to you guys with my take on it.