https://www.youtube.com/watch?v=w5SRH6Ac1LI&t=25s Love that movie. I didn't remember that so I found the scene. The character's joking / trying to mess with the other person. "You gotta put that thing to your chin. It makes your head into an antenna, so... I think it gives you cancer but you find your car faster. I mean, you don't live as long but you get where you're going quicker so it all evens out. Just a suggestion." At 5:15 in that video she tries it and it works.
Depends. There is lots of irrational fear with this and as far as I know, no solid proof for harm, but there is extra electricity flowing in your head, because of the transmission of your phone. I don't like talking on the phone that much anyway, so I do not care so much, but if I would talk for hours, I would use a headset (also for ergonomic reasons).
I suspect not. Its a short burst of rf and not done very frequently. (I use this technque with an key fob near an open mouth probably 4 times a year.. Thanks Car talk.
RF is harmless below the point where it directly heats tissue.
Having a full strength cell tower transmitter inside your home is not safe due to the intensity of the transmission, it will directly heat tissue inside your body.
I think the distinction/point is that it's not harmful in the 'this might give you cancer' way that ionizing radiation sources will. Worst case, you get an RF burn... which is not great, but it's effects are immediate and obvious, unlike ionizing radiation which is much more insidious.
Microwave RF that is somewhat directional behaves a lot like laser light.
If you were to step into the beam carried by a waveguide for something like a powerful TV transmitter, it will cook you through like a death ray out of science fiction. Fortunately it's not actually collimated, so just a few feet away the energy is barely enough to cook your retinas faster than your blood supply can cool them (which can cause blindness). Otherwise, yes, it's much like infrared heating effects. If infrared penetrated a few centimetres deep, anyway.