The only resolution authority I have not experienced but have second hand information had resulted in structural damage to the horizontal stab of a DC10-30. There is no time (and should not be considered) to contact ATC until the RA has been performed, this was at cruise over Columbia.
High altitude reporting over countries that still allow communications other than English contribute to this. FANS is supposed to be the solution.
None the less TCAS is vital as the priority to allow a reactive solution, communication falls second as a proactive and safer method to avoid airborne collision.