DTMF stands for Dial Tone Multi-Frequency. It is the standard by which telephone providers translate the individual button presses for the dial pad. Each key on the dial pad creates a tone of a different frequency. In the past, these tones triggered events in the phone’s system. Because VoIP providers interact with the landline phone system, they use DTMF tones on connected phone calls. This means you can navigate old-school automated services.