One thing that's odd about this is that it's phone only, so they need your phone number. It would be a million times better if it were an android app you could

One thing that's odd about this is that it's phone only, so they need your phone number. It would be a million times better if it were an android app you could sideload onto any device and use anonymously; exchanging your contact details anonymously. It's hard to see how whatsapp can legally/technically defeat a request for `which contacts does this person communicate with`. The same goes for the Signal app too. Am I missing something here? Clearly none of the protocols require phone numbers, so why do the implementations?