So... you're just confidently wrong enough to be annoying.

You cannot interchangeablly use different parts of the spectrum to communicate.

Yes you can. Different frequencies have different ways that they interact with matter, and those differences make them more or less effective and practical with certain methods of communication, but there is nothing that stops a visible light from using modulation to pass a signal, nor a radio beam from sending binary signals by on-off keying or frequency-shift keying. It's just a sliding scale of effectiveness.

The reason that radio is used to broadcast signals is because the wavelengths at their frequency are long, which allows them to spread far, through and around objects with very little of its energy being absorbed by air and objects. Visible light won't pass through most matter, but radio and infrared can. But as for using modulated broadcasts, there is no frequency at which electromagnetic waves can't physically deliver information through amplitude modulation (AM) or frequency modulation (FM) if there's nothing blocking the light. Radio waves just have less issue penetrating into homes, offices, cars, etc. and carrying for miles through air and leaves and buildings from its towers where it's signal is needed, so we use it that way.

And there is no frequency of light that you couldn't send a binary signal by turning a beam on and off either. But we use visible light in fiber optic cables, for example, BECAUSE it doesn't pass through materials well. A beam of light can be sent down a fiber optic strand, bouncing internally through reflection along the cable, and light in the same spectrum can't enter the cable from the outside due to its opaque sheathe. A beam in the radio frequency would behave more or less the same way in a fiber optic cable, but because radio waves can penetrate the sheathe, you would degrade the signal with lots of noise over long distances. It's not that you can't, it's just that it's less effective with that method.

While we're at it, electromagnetism is used in several other ways to communicate that are not limited to these methods. IR blasters, WiFi, LiFi, NFC, RFID, Microwave communication, Bluetooth, Cellular signals, etc. Another reason for specific frequencies being used in different ways is to regulate traffic for these different technologies too, to limit noise and interference as much as possible.

From a physics perspective there isn’t a reason you can’t utilize other parts of the em spectrum for radio communication. Radio can be amplitude (AM) or frequency (FM) modulated, or now even digital. The same techniques can be applied to other bands. The different groups, radio, microwave, come from human categorization, as well as different engineering approaches related to technical limitations.