offline

Someone that Off-line they are off from the line

FOR PHONE CALLS
Narrator: Sorry, the person you're calling is currently offline.
FOR LINES
(inside a party: there's a cupcake stand that has THE ULTIMATE RAINBOW CUPCAKE)
Person 1: I will wait until it is my turn
Person 2: Same!
Person 4: *saw person 3 go away from the line, thinking he didn't want the cupcakes* In Mind: He's off from the line now, TIME TO STEAL IT

offline

when someone from the other line turns off from you so it's called Off-line

Person 1: Hello, what can I get for you
Person 2: *offline*
Person 1: again...