code: func ToPhone(theString, delimiter string) (string, error) {
  	f := New(theString)
  	f.removeNonDigits()
  
  	if f.length < 10 {
  		return "", errors.New(lengthError)
  	}
  
  	var buffer bytes.Buffer
  	count := 0
  	switch f.length {
  	case 10:
  		buffer.WriteString("(")
  		for _, i := range f.theString {
  			count++
  			buffer.WriteString(string(i))
  			switch count {
  			case 3:
  				buffer.WriteString(") ")
  			case 6:
  				buffer.WriteString(fmt.Sprintf("%s", delimiter))
  			}
  		}
  	case 11:
  		for _, i := range f.theString {
  			count++
  			buffer.WriteString(string(i))
  			switch count {
  			case 1:
  				buffer.WriteString(" (")
  			case 4:
  				buffer.WriteString(") ")
  			case 7:
  				buffer.WriteString(fmt.Sprintf("%s", delimiter))
  			}
  		}
  	default:
  		return "", errors.New("non US number given")
  	}
  	return buffer.String(), nil
  }
docs: // ToPhone will format the provided string as a Phone Number.  Only supports
  // US numbers currently.