[BenMcr]

If you recieve an incoming call and the person phoning you is using a corded phone you can't hang up

If you put the phone down and then pick it up again the other person will still be there.

So all they have to do is stay silent on the line and it seems like you have no dial tone.

Also you can make the line redial if you tap the 'hang up' switch on a corded phone.

I'm sure there are computer systems than can do all of this automatically lol