In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands.
The term voice frequency can also be used to refer to the band of the electromagnetic spectrum between 300 and 3000 Hz.
This information is sourced from Federal Standard 1037C and MIL-STD-188.