Granted Patent
Utility
US 4,775,975 · App. 06/802,172
Dial tone detection arrangement with a detection notification feature
Inventors:
Jeffrey A. Cromwell, Robert Ducharme
Patented Case
View Patent ↗
Granted: Oct 4, 1988
Filed: Nov 26, 1985
Inventors
Jeffrey A. Cromwell
Robert Ducharme
Assignee (at issue)
American Telephone and Telegraph Company, AT&T Information Systems
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.