Having recently bought a G1 gphone I have noticed that there is no MSN messenger or windows live messenger client included with it. In the Android marketplace there are various applications which claim to do MSN but I have not had any great success with them. Some seem to have been affected by recent operating system upgrades.
I also tried Ebuddy from the web browser but could not get it to work because of problems with the way it requires pop ups.
So far the only way I have found of doing MSN messenger is by using their old mobile interface which is located here.
Click Here to log in using the built in web browser in the gphone.
Its not ideal but it works.