num, err := libphonenumber.Parse("6502530000", "US")

// num is a *libphonenumber.PhoneNumber
formattedNum := libphonenumber.Format(num, libphonenumber.NATIONAL)

// Parse the number.
num, err := libphonenumber.Parse("1234567890", "US")
if err != nil {
        // Handle error appropriately.
}

// Get the cleaned number and the length of the area code.
natSigNumber := libphonenumber.GetNationalSignificantNumber(num)
geoCodeLength := libphonenumber.GetLengthOfGeographicalAreaCode(num)

// Extract the area code.
areaCode := ""
if geoCodeLength > 0 {
        areaCode = natSigNumber[0:geoCodeLength]
}
fmt.Println(areaCode)