Unable to connect to MSN Messenger service?

I am getting an 80072745 error code when i try to log into msn messenger...it seems unable to repair a problem with my default gateway. I believe this problem is directly connected to the fact that i have a mobile broadband connection - primarily a T-Mobile Web n Walk usb stick. I did have problems with Yahoo Messenger as well but I solved that problem by setting its connection as going through a HTTP proxy, Im wondering if i can do this with MSN Messenger as well....can anyone tell me how I do this, Ive tried several things but with no success so far