Device for adding intercom functions to a phone system
May 4, 2007. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent ReferencesHold-plus-intercom for single-line stations Modular, expandable intercom system for a multiple-station telephone subscriber installation Tone selective key telephone intercom system including digital tone detector Home communications and control system Key telephone system Telecommunications systems Telephone intercom system Programmable telephone switcher Patent #: 4674115 InventorsAssigneeApplicationNo. 07/045321 filed on 05/04/1987US Classes:379/393, Hold circuit379/160With connection of intercom station to subscriber lineExaminersPrimary: George, Keith E.Attorney, Agent or FirmInternational ClassesH04M 1/72 (20060101)H04M 1/723 (20060101) H04M 9/02 (20060101) AbstractA device for adding intercom functions to a residential or small business phone system uses existing telephone equipment and wiring. The device attaches to the incoming telephone line to switch telephone calls and generate user coded ringing signals. The invention allows the user to simultaneously use existing telephone equipment as an intercom system and for normal outside telephone use.Other References
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