This is an old trick. It is easy to make the line go dead. With a land line only the caller can disconnect the call so he asks you to try and call someone else and by the time you hang up and pick the phone up he has hit mute. You are still on teh phone to him and he can hear you bashing the buttons. All he has to do is wait for you to put the phone down again and ring back.
Simple. You can try this at home.
Edit: Oops! I should learn to read the whole post before typing