Things you see in movies aren't meant to be made real. In movies, the pin is good for theatrical effect, because the actor recites his thoughts to the camera. There is no camera in real life, instead there is other people
I’m curious what movie you’re referring to? Even in Her, Theo just puts his phone in his shirt pocket with the camera exposed so Samantha can see things.
Correct me if I'm wrong GO, but I'm pretty sure he's referring to StarTrek, by comparing this pin to a combadge.
Star Trek (TNG, but the other shows too) had badges they wore on their shirts as communicators. Helped for story telling, because as opposed to a phone, the com badge would play the other person’s audio loud for all to hear.