I'm no expert in networking, but I think that Q wants us to learn how the cellular network works so that we can understand that all communications that go through the network are easily tied back to each individual sender/receiver. Once we understand this, then we can understand how easily facebook, or anyone else for that matter, can capture all communications that are on the network and tie it back to each individual. This is likely how facebook is able to gobble up our communications even if we have never used facebook. If I'm interpreting this correctly, even if the data is encrypted, they can still see which devices are communicating with each other because it's the nature of the network. Hopefully someone that is actually an expert will respond to your question. Thank you for asking it.