Contact Net Llama! for any questions related to the modules for kernel versions 2.2.15 & 2.4.x or higher.
UPDATED 05/23/02

If anyone is interested I will tell you how I finally got my pctel winmodem to work.  Actually I essentially followed the directions in the readme file but also had to make a few assumptions.  

Before proceeding, verify the status of your modem at this unofficial (yet accurate & useful) PCTel Linux database:
http://pctelcompdb.sourceforge.net/display.php
If your modem isn't listed there, odds are, it will not work with the PCTel drivers on this page.

Choose your kernel version:
2.2.0 - 2.2.14            2.2.15 - 2.2.19            2.4.x
 

For kernel versions 2.2.14 or earlier (only 2.2.x kernels supported):
After unzipping either the file MODEM.ZIP or hsp56-linux-1.tar.gz, from
http://www.idir.net/~gromitkc/winmodem.html
NOTE: This module only works with kernel versions 2.2.14 and earlier.  See below for 2.2.x kernels after 2.2.14.

I got some files and the following folders:
lib, src, and include.  Earlier on I treated these folders as separate entities - mistake.  I finally caught on that I should be transfering the contents of these folders to the /lib, /src, /include that exist under /usr.
Alternatively, the directory structure could be manually created inside of any directory, so that it includes
/lib /src & /include .

1a) Ran "make" under $/src/serial.
2a)  Went to $/lib where I found the pctel.o file.
3a) You must be root to do the remaining steps.  Then typed "mknod /dev/ttyS15 c 62 79".
4a) Set a symbolic link with  ln -s /dev/ttyS15 /dev/modem
5a) Typed "insmod ./pctel.o".
6a) Opened Seyon and it confirmed that my modem was recognized - a joyous moment.
7a) Add the command from step 5 above to the bottom of your /etc/rc.d/rc.modules file so that the module gets loaded automatically at bootup.  Be sure to specify the full path to the pctel.o module so if you kept the module in /root/stuff/ you would add "insmod /root/stuff/pctel.o" to the file.

I set up kppp and set the connection speed 4 times that of my modem ie 200,000 or something like that but got only a connection of 9600 and there was *no* data transfer.  Embarrassingly enough I did a typo on the dns - I trimmed down the connection speed to 100,000 and voila!! My modem performed every bit as well as under windows.

For kernel versions 2.2.15 or later (only 2.2.x kernels supported):
1b) Download these modules (single tarfile) (in Netscape, right click on the link and choose Save Link As):
pctel.tar.gz

You will not need both modules, however I have not found any documentation as to which one works with which PCTel modem.

2b) Follow steps 3a & 4a from above, if you have not already done so.
3b) Run "insmod -f ./pctel_pci.o" and ignore the kernel version warnings.  Verify that the module has successfully loaded by running the 'lsmod' command.  You must be root for this step.
4b) Configure KPPP or KsaferPPP for your ISP, and make sure that it is using the /dev/modem serial port.  Attempt to connect.  You may get an ominous "MODEM HANGUP?!" error the first time, but try again, as this appears to be a very minor bug in the module.  If after a short while you are connected, then all is good in the world, and the Linux gods have smiled on you.  Just one step left, jump to step 6b.  If it still fails, do not give up hope yet, see step 5b.
5b) You must be root for this step.  Run 'rmmod pctel_pci' to unload the bad module.  Then try steps 3b & 4b again with the other module, pctel_hsp.o .
6b) Add the command from step 3b with the module that worked for you to the bottom of you /etc/rc.d/rc.modules file so that it loads automatically on your next boot up.  Be sure to specify the full path to the module so if you kept the module in /root/stuff/ you would add "insmod -f /root/stuff/<module_name_here>" to the file.

For kernel versions 2.4.x (only 2.4.x kernels supported):

1c) Download the module:
pctel-0.9.6.tar.gz
2c) Read the README INSTALL & FAQ before doing anything else.  You will not have your questions answered if they are already covered in all of these documents.
3c) I will strongly recommend using this module *ONLY* with a 2.4.x kernel that you have built from source.  I build my own kernels, and you should too!  Sometimes vendor (Redhat, SuSE etc)-built kernels have patches that prevent functionality of third party software.