> Messages by default are encrypted in transit. Client to server.

By this metric Facebook and Google are encrypted, because TLS. Sorry, Telegram's messaging is an attempt to mislead users, plain and simple.

> The library IS used for all encryption.

They could chose to use TLS for for almost all chats, and instead they've "invented" MTProto. Why go with MTProto?

> As far as I can tell from casual use the other end does not need to be online per se.

You are wrong. Phone on other side has to accept "secret chat request" (no user interaction is needed). Until its accepted, initiator's app interface is blocked with a spinning circle. And to add insult to injury, one can't initiate secret chat from desktop client.

> Telegram client(s) are also open source.

Yes, it is very refreshing to be able to verify that they can read all of my messages. /s

> The comment was about the server and interoperability with other clients.

Signal leadership explicitly stated that they care about secure comms and don't care about ecosystem around the chat. You can create your own client, you can't market it as Signal because that might "endanger lives".

> - The phone bits in your and the other commenters response sound a little bit handwavy to me.

I issue you a formal apology on behalf of HN hive mind. /s

On serious note - palata's point is right, but a bit outdated. Functionality is still there, but it became opt-in. New users have phone number automatically hidden and phone number is collected only as an anti-spam feature.

I'll repeat my point again. Telegram is a honey pot of messengers and nobody should use it.