Key selector switch for telephone sets

Key system protective apparatus

Key telephone adapter for electronic telephone switching system

Key telephone apparatus

Key telephone apparatus

Key telephone apparatus with automatic call distribution...

Key telephone area voice paging circuit and method

Key telephone communication path interface

Key telephone exclusion circuit

Key telephone hold arrangement

Key telephone intercom line system

Key telephone interface

Key telephone lamp control circuit

Key telephone line circuit

Key telephone line circuit

Key telephone line circuit tone-on-hold arrangement

Key telephone line shunt detector circuit

Key telephone off-premises line circuit

Key telephone privacy circuit

Key telephone set having interchangeable units