To find out what kind of software modem you are using, go to linmodems.org, read the page, and download the scanModem tool (which will only recognize PCI and USB modems, not ISA modems). Copy it to your desktop in your Ubuntu machine, then open a command line and enter:
$ cd ~/Desktop $ gunzip scanModem.gz $ chmod +x scanModem $ ./scanModem $ gedit Modem/ModemData.txt
The program gunzip will decompress the file, chmod will mark it as executable, and ./scanModem will run it. If it tells you to do something as root by issuing su - root, instead just enter the commands it wants following a "sudo", e.g. $ sudo modprobe snd-intel8x0m. scanModem will scan your modem and tell you what it is and how to configure it. It will not configure it for you. But after running, you will see a number of new folders, including a Modem folder. Read 1stRead.txt and ModemData.txt in there, and see if you modem was recognized. This is admittedly not a straight-forward read and might need some more reading around on above mentioned page to find out which drivers your modem needs. Then scan through the following sections to find out about the easiest way to install that driver under Ubuntu.
Note: For many of the following drivers, you will need to enable the universe and or the multiverse repositories. See AddingRepositoriesHowto. This requires you to have working network connection. You can also search for packages to download in another system and transfer to your Ubuntu installation at http://packages.ubuntu.com/ . Be careful with the dependencies... Check out this forum post for another way to get packages using the LiveCD on another system with network connection and a CD burner: http://www.ubuntuforums.org/showpost.php?p=893732&postcount=6
Now that you know what modem you have, please return to DialupModemHowto to continue.