Granted Patent
Utility
US 4,868,872 · App. 07/230,078
Telephone tone detector
Inventors:
Melvin J. Roberts, Frank Dea
Patented Case
View Patent ↗
Granted: Sep 19, 1989
Filed: Aug 9, 1988
Inventors
Melvin J. Roberts
Frank Dea
Assignee (at issue)
Mitel Corporation
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.