I personally recall people ocassionally being able to hang up one phone before picking up a different phone if they wanted to take the call in a diffent location in the house. Although, I don't remember it ever being very effective, over time (in my corner of the US), it became never effective, so you'd just leave the first phone off the hook and have to hang it up later.
On your smartphone, it's easier to not fall in this trap, as the screen is making it harder to type a phone number while the call is still going.
It used to be the case that the party who made the call - being the party who is paying for it - was solely responsible for terminating it; then timeouts were introduced; and on many landline exchanges there is still a timeout before the call is actually terminated if the callee hangs up but the caller does not - although these days it is just a few seconds, that may still be long enough that you stay connected to the original caller if you hang up then immediately try to place a call.
Google "called party clear" for gory details.
In the Netherlands, in the 80s-00s at least, hanging up cleared your line, so picking it up again would get you a fresh dialtone even if the other side didn't hang up (and the other side would get a modified "busy" signal if you hung up on them).