dln949 Hello dln949, I'm not sure if this is the case with all carriers, but I know with Verizon when you place a call and the recipient's phone beeps in your ear, that is an indication that they are on the other line. If I'm not mistaken, it's a slightly longer ring with a beep at the end of it. (Call waiting).
Also depending on their setup, your call may go straight to voicemail if the recipient is on the phone.