This .deb is the Conexant driver for the 1505n officially supported by Dell, however it also works in the 150 because it's the same D110 Chipset.
Conexant Modem .deb from Dell's Website
You can wget in a terminal (default save is to your home login folder /home/YOUR USER NAME)
It's good to see Dell involvement is giving back to the open source world. I wish I could test it out but I don't have a phone line or access to a dial-up account. If you get it to work, let me know how it went.
edited by pHreaksYcle