code: public String toUrl() throws TwiMLException {
          try {
              return URLEncoder.encode(toXml(), "UTF-8");
          } catch (UnsupportedEncodingException e) {
              throw new TwiMLException(e.getMessage());
          }
      }
docs: Convert TwiML object to URL.
  
  @return URL string of TwiML object
  @throws TwiMLException if cannot generate URL