Apparatus and method for detecting telephone line status
Busy line display method
Communication system having dynamically assigned station set but
Communication terminal apparatus
Dealing call terminal device
Device for detecting operation state of telephone hook switch
Extension ringing arrangement key telephone system
Key telephone system
Local switching system
Method for exchanging a buzz signal between keyphone subsets
Multi-line telephone communications system
On-hook customer premise equipment alerting signal detection
Page-mapped multi-line telephone communication system
Private branch exchange and telephone switching system
System and method for provisioning an extra line on demand...
Systems and methods for voice and data communications...
Telephone extension switch hook state detection system
Telephone line status circuit
Telephone system
Trading telephone