Access to Exchange 2003 (OWA) via mobile phone

Does anyone know what do I have to do in order to access Outlook Web Mail. I can browse all other sites but when I try my corporate web site I am not able to do that.
I can access only login page and when I submit user name and password and try to logon it states that the page cannot be found or this site uses frames but your browser does not support them. The Web access is working from PC without any problems
I tried to do this with Nokia 6131.