The examples I had in mind is when someone is on the phone in their office and another person walks in, prompting the person on the phone to say "I'll call you back". But it's true that it also happens when there is another call waiting - a function that I never use (because I don't like being interrupted in the middle of a conversation). Hollywood loves to use the juggling with a second call function to cause awkward situations when the person doesn't switch properly to the other caller and inadvertently says something they shouldn't to the wrong person.
In the series I have been watching it isn't kids who are talking like that, but professionals like lawyers, FBI agents, politicians and the like. In the same situation I would ask the visitor to wait until I have finished my call.
It all depends on the circumstances. I was speaking of situations at home. I could and can cook a whole meal, or iron a basket of clothes while talking on the phone to my mother or a cousin or a good friend.
Between work and children and intellectual pursuits, I had to fit my social life into the nooks and crannies of my life. I can remember keeping the phone crammed between ear and shoulder. Better technology made it easier. Perhaps it's difficult for men to understand it, but those calls could go on for an hour or more. Call waiting was essential. Maybe a child missed the late bus, or someone could get into an accident, or you're waiting for a call back from the electrician or doctor or whatever. Or maybe you just had a very demanding husband who would get totally bent out of shape if you didn't immediately pick up his call.
He was the same at work. If the phone rang more than four times somebody got dressed down or even fired.
Work is different and it also depends what kind of work you're doing. The time pressures, competitiveness, even the "office atmosphere" of a certain company can affect it. Area of the country can affect it too. I think quickly, speak quickly, react quickly by nature, but it was also the atmosphere everywhere I worked. Patience isn't natural to me. When I had to deal with clients from Atlanta I can remember getting so frustrated at how slowly they talked, and, I believed, thought, that I sometimes felt like jumping into the phone and dragging the words out of their mouths.
There's an expression where people say get it done in a "New York minute". That's a lot faster than a Georgia minute, or even a California minute!
If you're an associate in a very high pressure Northeast law firm working on a big deal, and a partner walks in while you're having a mundane conversation with the printing department you would absolutely NOT take the time to finish the conversation. You might indeed say, I'll get back to you, ok, hang up, and look very eager.
If you're working on a big case, and important information is brought to your desk or comes up on the computer screen, you might not take the time to explain to the person on the phone why you can't continue the conversation. The "work status" of the people involved also affects how you behave. If you're on the phone with the client, or a partner, or your boss, unless the building is on fire you're not going to interrupt the call. I'd go ballistic if some secretary or new associate were to come in and interrupt me with some irrelevant nonsense while I was on an important call. Sometimes they're even conference calls, which are really meetings. On the other hand, I've been known to "fib" and pretend my secretary just came in or even told the secretary to interrupt me to get rid of some nuisance on the phone.
I actually do remember one situation involving someone with whom I had to work but who was not directly under my control who had called me two or three times in a row, hectoring me about when I would give him my decision. The last time I hung up on him because he'd gotten profane. The phone rang again within a second or two. I picked up the phone and barked that I'd let him know as soon as possible dammit, and that if he called me one more time I'd....well, you can imagine. It turned out to be my section chief. He was a good guy though, and no shrinking violet himself, plus we had to deal with some pretty rough characters, so he said something like, yeah, right, you and who else, and laughed. I probably weighed 118 pounds soaking wet.
As for these police procedurals, they're all unrealistic to some degree or another. One that's pretty darn close to the real deal for local law enforcement is a show called Law and Order, either the regular show or the special victims unit, especially the earlier years.