1. Requiring a unique phone number for signup, and heavily restricting accounts which appear to have used a VOIP phone number for signup (including Google Voice numbers). Restricted accounts can't initiate conversations, so they can't really send spam.
2. Allowing users to report spammers that get past #1, and limiting the accounts of users that get reported.
For details, see: https://telegram.org/faq_spam
but for IM
While you enjoy your "spam free" service, some of us will have to work with the separate but not equal alternative. In case you haven't noticed, as the common communication environment has become more and more locked-down (starting with mobile, and now spilling over into desktop), fewer people are using open alternatives. Simply observing that open protocols exist doesn't make them an actual de facto alternative.
Are you paying for it?
I can be reached by telephone. What I don't have is a unique telephone number. This works perfectly fine for actual voice communication. If you think I can simply afford an extra monthly expense, you're wrong.
> You are like 0.0000001% of the market.
Made up statistics reveal your presuppositions.
There are a lot of people that don't have a unique phone number. It's a minority position, but that's kind of my point: chat services do not inherently depend on traditional phone numbers, and requiring one is going to exclude more people than you probably realize.
Are you in a country which doesn't have pay-and-go service?
And of course that statistic is made up. It was a joke.