enum DtmfSenderHighFreqency

Possible DTMF high frequency values.

References from:: DtmfSenderService;

`1209`	`FIRST_HIGH_FREQUENCY`
`1336`	`SECOND_HIGH_FREQUENCY`
`1477`	`THIRD_HIGH_FREQUENCY`
`1633`	`FOURTH_HIGH_FREQUENCY`

enum DtmfSenderHighFreqency