Current mode ring trip detector
Current source and off-hook detector
Custom telephone
Cycle-modulating type of dual-tone multifrequency generator
Data communication apparatus
Data communication apparatus including volatile and non-volatile
Data communication method and apparatus including volatile and n
Data storage apparatus
Data transmission apparatus having abbreviated dialing function
Deformable membrane keypad assembly for public telephones
Detecting whether a telephone line has been disconnected
Detection of both voice and tones using Goertzel filters
Detection of multifrequency tone signals
Determining the manner in which the wires connecting to a base s
Device and method for cleaning telephone number list
Device for automatically identifying DTMF and FSK for caller ID
Device for detecting DTMF tones
Device for detecting telephone line seizure
Device for detecting tones on telephone lines
Device for identifying line reversal/ringing signal of a telepho