This is a dreaded software modem and as such is not recognised directly by Linux. You can, however, install a SmartLink driver from
http://linmodems.technion.ac.il/packages/smartlink/ if you are prepared to implement a few work-arounds
and are happy to ignore the messages about your kernel being tainted. (The "tainting" is from proprietary code contained in the Agere modem software, and should not affect the operation
of your system in any way.).
Many thanks to Chris Bradshaw for bringing this driver to my attention.
First, download the latest version of slmdm. I have tested slmdm-2.7.10.tar.gz with Red Hat 8.0, and it seems to work fine. If you have problems with gcc versions or general setup, there is plenty of help and advice at the Linmodems home page.
To install, copy the downloaded file to /usr/local/ , do a tar -xvzf, change directory to slmdm-2.7.10 , then make and make install-amr.
Installation will automatically create the following entries in /etc/modules.conf:
alias char-major-212 slmodem alias slmodem slamrmo
options slmdm country=UK
Then do modprobe slamrmo and you will get all sorts of stuff about tainting the kernel, which you can ignore. You may also get messages about gcc versions used to compile, in which case it will not work, and you must seek help as detailed above.
Note that the installation will also have created a symlink from /dev/modem to /dev/ttySL0 , overwriting any symlink you may have had already (e.g. to rfcomm0 for Bluetooth). If this is not what you want, you will have to create a different symlink to /dev/ttySL0 manually.
You should also change the ownership of /dev/ttySL0 to uucp by doing: chgrp uucp /dev/ttySL0
Now you can test the modem using your favourite dialler. I used kppp to send "ATI" and received the following info:

If all seems to be working, you can try dialling your ISP. I was able to connect at 45.333 kbit/s without any problems.
Note: Because the Ethernet interface is integrated within the Toshiba hardware (i.e. not a PC card), the ppp daemon gets very confused when you try to establish a network connection through the modem card. You must explicitly disable the eth0 interface before dialling:
(su root) $ /sbin/ifdown eth0
This is a real pain, and I have mitigated it slightly by establishing 3 different networking profiles, one for home, one for office, and one for "remote" when I am not ethernet-connected. In RH8.0, the relevant file is /etc/sysconfig/network - for dial-up access you will need to change 2 lines:
GATEWAY=0.0.0.0 GATEWAYDEV="ppp0"
For Ethernet connection to your home or office network, the lines should show the IP address of your default gateway, and "eth0", respectively.
You may like to try my shell script for switching network configurations between home-office-remote(dialup), but please follow the README first.
Also, here is a shell script for automatically loading the SmartLink driver and setting up the correct symlink from /dev/modem. This is useful if you are using various different modem devices (internal, Bluetooth, PCMCIA...) and want an easy way of overwriting the previous configuration.
If you have problems with the SmartLink driver, and want to obtain information on Linux-compatible PCMCIA modems, visit this site.