MSN and YIM message launch URL?

[unlucky17]

So, there are custom URLs for AIM and Skype:

aim:goim?screenname=(username)
callto://(username)

If you click on them it will supposedly launch the appropriate program and send a message/call to that username.

Anybody know the URLs for Yahoo IM and MSN like this?

[johanafm]

http://en.wikipedia.org/wiki/URI_scheme contains both official schemes and non-registered schemes such as the ones you're after.