AFAIK you've always been able to bring your own phone. They just wouldn't unlock your subsidized phone after the contract ended (which I find unfair, but it's in the contract people signed, so...). Regardless, I think this line of thought is becoming too off-topic.

Why should the first party be serving content to people using third party apps that generate them no revenue? Just like websites are free to block adblock users, app apis should be free to block third party app users.

I'm not talking about cell phones. I'm talking about rotary dial phones back in the days of Ma Bell.