code: public void buyNumber(String country, String msisdn) throws IOException, NexmoClientException {
          this.buyNumber.execute(new BuyNumberRequest(country, msisdn));
      }
docs: Start renting a Nexmo Virtual Number.
  
  @param country A String containing a 2-character ISO country code.
  @param msisdn  The phone number to be bought.
  @throws IOException          if an error occurs contacting the Nexmo API
  @throws NexmoClientException if an error is returned by the server.