Tell me, can you have a Signal account WITHOUT giving them your phone number?

Can you sign up for Telegram without a phone number?

Yes: https://telegram.org/blog/ultimate-privacy-topics-2-0

Without "SIM card" and "without a number" are different things. Apparently you still need a number, a "blockchain-powered" number:

"[...] You can have a Telegram account without a SIM card and log in using blockchain-powered anonymous numbers available on the Fragment platform."

Irs super complicated to use. And you need an existing Telegram account to actually handle that cryptocurrency to buy these pseudo-numbers outside of the telephone namespace. Guess what you need to register those. An actual working phone number.

That's just buying a fake phone number, I don't see what would prevent you from using it with Signal the same way.

Not everyone is commenting on signal vs telegram here, it may just be an opinion that the phone number requirement is dubious from both entitites.

You still need a phone number to sign up

I'm not sure what the behaviour is now but certainly the default a while back was that anytime someone in your contacts joined Signal you would get a message. Imo this was a crazy behaviour that immediately told you something about certain people in your contacts in a very visible way (that they were on Signal). I couldn't tell from the settings whether this was now off by default.

Telegram has done and may still (I don't know personally) do the exact same thing. Stated noncombatively and without assumption about what argument you may or may not be making, but seems relevant to mention in this context. Astonishingly bad behaviour no matter which app!

Both do that.