Granted Patent
Utility
US 4,390,982 · App. 06/225,020
Digital PBX system
Inventors:
William H. Williams, Michael G. Burke
Patented Case
View Patent ↗
Granted: Jun 28, 1983
Filed: Jan 14, 1981
Inventors
William H. Williams
Michael G. Burke
Assignee (at issue)
International Telephone and Telegraph 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.