Your number can't support GPRS? Most bizarre. The N900 is a GPRS device so where possible you should make use of the available technology.

Have you read the fMMS thread?

You need to do a search for what the protocols are for msn. I have no idea on that one. Once you know what they are you'll need to find out from your provider what protocols are permitted (or not).

It might be a bandwidth problem, in which case you'll need better than WAP.

Follow those steps and if you're still having trouble post back with
- your APN details,
- info about the msn protocol
- and the accepted/banned protocols of your provider. Someone will be able to help once there's more to work with.

Is there a browser-based msn chat interface? Can you use that?