Do you stay on the line if you hear the dial tone?

I feel like I should know this by now, but generally, do you just hang up or can you wait and it will go through once the line of the person you are calling is no longer busy? Do you have to call again when the line is no longer busy in order to reach the person?

On my iPhone it lets me know when I have another incoming call, but lately I've been trying to participate in a radio contest where you have to be a certain number caller in line and I never know whether to hang up and try again when I do get the dial tone or if I can just keep it on the dial tone until it connects you after their line is no longer busy?

Let's get the terms straight: "dial tone" is the sound you first hear on a standard telephone to signal that it's ready for you to dial or punch in the phone number. "ringing" is the repeated sound you hear when the other phone is ringing to be picked up. "busy" is the beep that says the line is occupied.

If the line is busy, you need to hang up and try again. If it is ringing, you can stay on the line until someone gets around to answering it.