ATC stands for Air Traffic Control AND NOT transponder. Those are collectively various controllers which communicate with a plane by voice. Transponder sends code (sometimes with data about altitude, depending on the type of transponder) to ATC radar screen, but it is not ATC itself. CVR (Cockpit Voice Recorder) is just a sound recorder, it does not use an antenna. Nowadays, depending on the airline, planes use various two-way, usually Internet-based methods of communication with the company (typically by text with Flight Operations) while in the air, via tablets, laptops, faxes, telexes, sometimes phones, etc.
