Granted Patent
Utility
US 4,879,743 · App. 07/252,477
PBX and adjunct using multi-frequency tones for communication therebetween
Inventors:
Edmund T. Burke, Daniel H. Dawdy, Timothy M. Rubert
Patented Case
View Patent ↗
Granted: Nov 7, 1989
Filed: Oct 3, 1988
Inventors
Edmund T. Burke
Daniel H. Dawdy
Timothy M. Rubert
Assignees (at issue)
American Telephone and Telegraph, Co.
AT&T Information Systems Inc.
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.