For a normal consumer it's not a flaw. But if you are a journalist or in any profession where sharing number is a big NO then yes it's not a good design. Case

For a normal consumer it's not a flaw. But if you are a journalist or in any profession where sharing number is a big NO then yes it's not a good design. Case 1: me and my friend want to communicate on signal. If he messages me on Signal there won't be any way to know if that's actually him. I would have to call him and confirm if its really him. For a tech-savvy person who is like crazy about privacy this is not a big deal. But for a normal consumer this make them remove the signal. Case 2: You want to message someone who you already communicate via WhatsApp or calls on signal. Again from an average consumer point. Calling them and asking them for their signal ID is again inconvenient. Imagine doing this for 400 contacts if you try to move from WhatsApp to signal. There are other secure messaging app which doesn't require number or even email. But then again, you meet the person or call him and then get his id. Not sharing mobile number is really for few selected cases and those people form a very small percentage of the market. Having a feature similar to telegram where you share your number with selected people. Or have a disposal ID which can be used to start a chat and then dispose that ID so that it can'be used again or linked to your account. Something like this would make more sense and probably serve that small percentage of people as well. An ID which gets destroyed once it's used to make a connection. One time use ID only. This is a good way as well. Secret chats which stays on one device only, or you need separate credential for. I should be able to make a sample app like this. It can be a good demo project.