DtmfTone type

DTMF tone for PSTN calls.

type DtmfTone =
  | "A"
  | "B"
  | "C"
  | "D"
  | "Flash"
  | "Num0"
  | "Num1"
  | "Num2"
  | "Num3"
  | "Num4"
  | "Num5"
  | "Num6"
  | "Num7"
  | "Num8"
  | "Num9"
  | "Pound"
  | "Star"