I recently bought a SmartLink 56k Voice Modem (because the box said it had Linux support). It took me forever to finally install the drivers on my Mandrake 10.0 distro. Now it is set up, but when I use kppp to try and dial-up to the internet, a message appears that says "modem initializing..." and it stops there. What's worse is that the README says to install the Driver as /dev/ttySL0 and link it to /dev/modem. I do this, and it links, but everytime I restart my computer, /dev/ttySL0 no longer exists, /dev/modem is no longer linked, and kppp goes back to using /dev/ttyS0. I have tried contacting the manufacturers, but it seems like everytime I send them an email, it goes straight into their round file. Can anyone help me??? Any help is much appreciated!

Are you using a 2.4.x or 2.6.x kernel? I have the BestData 56K USB modem which uses SmartLink drivers and came with one that works with a 2.4.x kernel. With that one the device and link will stay between boots and regardless of wether the modem is physically connected or not.
The 2.6 kernel, however, requires a later version of the driver. I'm using 2.9.10, free download from SmartLink's website. The device file is only created when the modem is physically connected and the driver must be run as a daemon. I made myself a small script to run the command:

slmodemd --country=USA /dev/slusb0

I do this from a terminal window after KDE is loaded and before I run kppp.

Also, IIRC, the initialization string for the modem is ATZ.