code: func (pn PhoneNumber) Friendly() string {
  	num, err := libphonenumber.Parse(string(pn), "US")
  	if err != nil {
  		return string(pn)
  	}
  	return libphonenumber.Format(num, libphonenumber.INTERNATIONAL)
  }
docs: // Friendly returns a friendly international representation of the phone
  // number, for example, "+14105554092" is returned as "+1 410-555-4092". If the
  // phone number is not in E.164 format, we try to parse it as a US number. If
  // we cannot parse it as a US number, it is returned as is.