I think Microsoft are attempting to focus on more pressing matters at hand, I'm sure an official IM solution will be available once multi-tasking has been brought in.
I think it all has to do with the api's multitasking and that Microsoft is not going to release the messenger app until this is in the dev tools I think we might see something at mix in april if not we will see it in october ..
I agree they should have an app but I do in some way like microsofts thinking and they are not going to release the app unless its great .. this is why there are alot of stuff missing in WP7 because Microsfot is not reddy.
Of course there's no multi-tasking...so IM clients are kinda hampered unless Microsoft builds it into the OS.
