Another tidbit, based upon finding out which company the phone number belonged to: you could go to the library and access business directories. Think the yellow pages, only they were geared towards businesses rather than towards consumers. Print versions were broken down by industry, but electronic ones (on CD-ROM) were searchable. It was also a tool for looking for unadvertised jobs, since those directories seemed to be geared towards making cold calls (albeit, for people doing sales).