In the early 1960s, AT&T introduced a method of providing in-band signaling so telephone customers could place telephone calls. The system was called dual-tone multi-frequency, or DTMF. AT&T, through ...

Excellent to remotely control via GSM the activation of engines, lightening or watering systems and alarm systems. It sends commands through SMS as well as with DTMF dual tones and allows you to check ...