I suspect that depends a great deal on the modem. The modem that I use has a web interface that can be accessed through http:/10.1.1.1/ so the various web scraping tools such as LWP and WWW::Mechanize could be used to access the information.

It may be that someone has written code for your particular modem and if you mention the modem type you may get the information you want. Otherwise, go read some documentation (modem documentation and the modules mentioned above). :)