FWIW, I think you can just get a Google Voice or other short-term burner number to sign up for Signal, and then never worry about it again. Signal's an order of magnitude more trustworthy than the other messaging players and have built out a good base of features at this point. (telegram specifically is a joke... proprietary closed-source encryption is a recipe for disaster.)

I would strongly advise against picking a tiny new-comer without some serious research beforehand... They're not battle-hardened, so will typically be less reliable than any of the existing larger players.