There seems to have been an official iOS app at one point, although I’m not sure where you’d find that now (it’s probably long gone from the App Store), and some third-party apps for Android, so it was definitely possible to access Windows Live Messenger from those platforms.
However, they’re new enough that they wouldn’t be supported by Escargot for the time being, because they use a more modern protocol. I’m also not sure how you’d change the addresses they connect to, but that could be looked into if copies of the apps were available.
Also, further discussion on this topic @ Escargot MSN in smartphone?