I always use and highly recommend a US Robotics external modem for my
dial-ups. For one thing, my US Robotics external modem can be swapped
out from my Linux box to my Windoze box and of course you can plug it
in to a Mac (you need the Mac cable, though).

Currently on the Linux Ubuntu Fiesty box, I am using the US Robotics
33.6k Sportster external fax/modem, model 0413, manufacture date 1995.

My other one which my Windoze box is running, it is a US Robotics 56k
V92 Sportster external fax/modem, model 5686manufacture date 2002.

I believe they are both doing the same thing with the Linux machine.

These modems plug into the serial port of the PC computer. I am using
a dial-up connection.

I can usually get Linux to log-in after a fresh install, but that is a
30-min. chore or so.

Question: Does Linux have something like "Norton Rollback" or that
useful feature in XP, "System Restore"? Maybe I could 'rollback' to a
previous setting?

The problem typically occurs if I have to shut down inadventently, or
if I keep my modem turned off when I turn on the Linux box, and I
guess that confuses its settings or parameters.