Just thought I'd point out, that MySpace is also currently working on a MySpace IM application. Similar to the Facebook app. Here is a little info. about it. I know this doesn't help anyone right away though.

MySpace is working on a Windows Mobile app to provide near desktop experience on a phone. The app will be available on Windows Mobile version 6.1 (or 6.5) phone by summer’s end.
The app then will be featured on Microsoft Windows Marketplace. Some committed manufacturers such HTC and LG will install the app on their new Windows phones.
Since MySpace endorses
Microsoft Silverlight for their application platform. I am not so sure if Windows Mobile will have Silverlight support by then.