I have motorola sm56 internal modem what i have to do to access net from linux
You need to configure your dialer under linux. If you are using KDE, try the kppp command. It should be somewhere under the Internet tools menu.
I suggest you do a search on google. You will surely get much clear idea on how to go about it.
What distro you are running ..?
You should check This site and Motorola's Softmodem Drivers page ...