Большой англо-русский и русско-английский словарь
dial tone
Англо-русский словарь технических терминов
tone origination, tone(-frequency) ringing, voice-frequency ringing, frequency signaling, harmonic signaling
Русско-английский политехнический словарь
tone origination, tone(-frequency) ringing, voice-frequency ringing, frequency signaling, harmonic signaling