we're a 24 hour pharmacy, so no one takes call.
however, in other departments in my hospital...if someone is on call and they are called in, they are paid for 4 hours [no matter how long they are there....could be 20 minutes, could be 2 hours]...if it exceeds 4 hours, you are paid for however long you are there.
no one is paid for just "being on call" unless they are actually called.