0 a continuous sound that tells you that a phone is connected to the phone system and is ready to be used
1 the sound that you hear on a phone when you pick it up, before calling a number:
I got the dialling tone and several times dialled the number he had given me, but nothing happened.
To indicate to called parties that they have waiting messages, the exchange sends an interrupted dialling tone to them when they take their telephone off-hook.
