Just a couple of details would help. I assume we are talking about an analog dial up modem built in to the laptop.
The make/model of the laptop.
The distribution/version of linux you are running.
The output of the console command lspci. This should show what chipset the modem is based upon.
In the mean time you could try searching the internet using the information to search for some information too.
These are good starting points.
http://www.linux-laptop.net/
http://www.tuxmobil.org/
