In the comics, after the events of Extremis, Tony has a telepathic connection to his technology as a result of modifying and "engineering" the virus to suit his needs. This link provides him with effective technomancy powers including some levels of silver age esq tech-precognition. This being said, Tony never contracts extremis during the events of Iron Man 3 in the MCU thus no silver age powers.
However, Tony can be seen in this same movie, experimenting with motion, retinal and gesture controls. Its feasible that a combination of minute body gestures (never visible from outside the suit) tone (which can be noticed in his dialogue) and retina tracking could be used to provide the split second switching between talking to Friday/Jarvis, radio communication, and local announcements.