Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Modem Controller
As found in IBM Thinkpad T42 series laptops, and in Toshiba laptops such as the Satellite 2450.
A few linux-on-toshiba pages, such as this one, suggest that a smartlink driver, found here will do the trick. I've yet to confirm this.
ThinkWiki (http://www.thinkwiki.org/Modem) also has some suggestions
For Ubuntu users, check out the sl-modem-daemon package.