code: func IsAlphaNumber(number string) bool {
  	if !isViablePhoneNumber(number) {
  		// Number is too short, or doesn't match the basic phone
  		// number pattern.
  		return false
  	}
  	strippedNumber := builder.NewBuilderString(number)
  	maybeStripExtension(strippedNumber)
  	return VALID_ALPHA_PHONE_PATTERN.MatchString(strippedNumber.String())
  }
docs: // Checks if the number is a valid vanity (alpha) number such as 800
  // MICROSOFT. A valid vanity number will start with at least 3 digits and
  // will have three or more alpha characters. This does not do
  // region-specific checks - to work out if this number is actually valid
  // for a region, it should be parsed and methods such as
  // IsPossibleNumberWithReason() and IsValidNumber() should be used.