Services requireing a mandatory phone number are ridiculous IMHO. Why do I need a phone number to set up an account on WhatsApp, Signal, Telegram etc.? And Telegram has a one phone number = one account policy. If I want two accounts, I need another phone number. SMS is sent across networks I don't control or trust (telcos), with no transport security, no verifiability of sender (what's the SMS equivalent of DKIM again?), no end-to-end encryption, and can be spoofed. We've already seen SMS 2FA recovery codes being hacked by socially engineering telcos. In addition Signal/WhatsApp/Telegram only allow one account per device. Want to have one account/persona for serious work and family stuff, another for bullshitting with friends, and another for giving to random potential stalky people you meet on Grindr/Tinder etc.? In the Signal/WhatsApp/Telegram paradigm, you can't have multiple personas - you are the arbitrary phone number your telco gave you to use on your one device, and you can't be anyone else. You can't have a second account set up on my phone with a fake name, so that some random person so you can chat to a random person you've just met with less risk without revealing the real name and profile image you use with your other contacts. Hell, I remember the AOL CDs from the 90s offering you "five different user personas FREE" etc. The pitch for the Signal/Telegram/WhatsApp model of secure chat app: "You too can have perfect security from the evil nasty NSA/GCHQ. First off, you sign up with your phone number, and then you give your phone number to everybody who you want to be able to contact you." The developers evidently didn't try that one out on many domestic abuse or stalking victims. For practical pseudonymity, a throwaway Gmail or Yahoo email account is far easier to acquire and maintain than a second phone number, a second phone handset and so on. The problem with Signal's threat model is that it protects you against the security services at the cost of not protecting from a jealous ex, a controlling abusive partner, an obsessive you met on Tinder who can't take no for an answer, a homophobic fundamentalist family member wanting to out you etc. - the actual people likely to cause you a significant problem when your day-to-day opsec fails.