Actually I don't know if there exist a command line replacement for msn messenger but there exists a web site which allows you to comunicate with others in yr list without having to install msn messenger - just yr web browser (just needs a javascript enabled browser). The link is:
http://www.e-messenger.net/
There is a graphical version of links (I don't know if it supports JS or not) so you may want to try it with this version of links.
type:
links -g
http://www.e-messenger.net/
Khalid El-Gazzar