Today, the only place where ultrasound is used for communication is underwater. However, this wasn't always the case. The very first television remote controls used ultrasound to communicate with the TV. As seen in the picture below, when a person would press a button, a hammer would strike a resonant bar, emitting a characteristic frequency.

Today, ultrasonics are used in many, many other ways, such as in cleaning and sterilization, collision detection, medical imaging, and even beer brewing.

Wireless communication has wholly fallen into the domain of IR and RF. However, many people forget that ultrasonic sound can also do that job. If an environment, for some reason or another, is not suited for IR or RF (possibly, both of those might already be in use in a room), ultrasound might provide an easy solution. Of course, sound travels around 330 m/s, which is appreciably slower than IR or RF, but that will not be a hinderance on a large number of applications. Luckily, if we want to now send data through ultrasound, we can build off of the work done in IR and RF. For instance, the data protocols that are used in IR and RF can be used with ultrasonic communication as well.