A good solution is paid registration. Telegram did an experiments for this, but they asked too much (about $10-15 for not requiring a phone number) and you need

A good solution is paid registration. Telegram did an experiments for this, but they asked too much (about $10-15 for not requiring a phone number) and you needed to buy their weird cryptocurrency. If Telegram asked about $4 in BTC for anonimity, I would gladly pay for it. It's interesting that this experiment shows how valuable is knowing your phone number and identity.