Agreed, #SMS isn't a silo, although not a freely accessible protocol either; it's only available at the whim of the carrier. And Google's new Chat uses RCS, supposedly Rich Communication Services, which will be equally controlled by carriers. But my suspicion is that, unlike SMS, Google will become the only app vendor for RCS protocol messages. My 5 year comment was based on the expected lifespan of Google projects. Google Mail has been around for a while, Google Buzz and Wave not so much.