Thanks alot Jone C. I have tried Kanotix and it does as you said. However, I am doing a remaster of knoppix 4.0.2 and trying to have sl-modem to work as a default modem exactly as in Kanotix. I have installed linux-source-2.6.12 package and compiled it. Then I did the following at the top of the folder /usr/src/linux-2.6.12:
make-kpkg modules-image
and got the following package:
sl-modem-modules-2.6.12_2.9.9d-7+10.00.Custom_i386.deb

I installed it and it did work. I connected to the internet. But, after rebooting my PC, the sl-modem-deamon dies imeadiatly. I tried to retart it several times. It retsarts but dies again. I checked the /dev/modem and /dev/ttySL0 links. Both are there but not linked to any other device. I hope some one can help here.