WOW!! It really does vary in each airline.. I was thinking about leaving my airline for another one, but I dont think I have the room in m head to change all the ding dong meanings! J/k..
In my airline the DING DONG is an audio alert to inform CC that the CSM/Purser whatever u want to call them is making an Interphone call to all crew stations. After taxiing this ding dong is a phone call to insure all doors are armed and cross checked.
The same just after u touch down.. except its to ensure doors are disarmed and cross checked!