Of course they will respond to warrants, they have to, and nowadays they have the infrastructure to forward all traffic to law emforcement's servers in real-time.
We're discussing this in regards to an article where the obvious "solution" was found by the government to this very approach. You're free to build it that way and we're free to put you all in jail afterwards as a result. Rubber hose decryption at its finest.
Phone operators are heavily regulated and licensed, and this is a legal requirement and a requirement of their licence. Complying with lawful warrants is also obviously a legal obligatuon.
