DtmfTone type
Nada DTMF untuk panggilan PSTN.
type DtmfTone =
| "A"
| "B"
| "C"
| "D"
| "Flash"
| "Num0"
| "Num1"
| "Num2"
| "Num3"
| "Num4"
| "Num5"
| "Num6"
| "Num7"
| "Num8"
| "Num9"
| "Pound"
| "Star"