actually....the three melodic chimes are a FA to purser call. Its sounds on the entire airplane and the purser can answer from the nearest phone. This is only on the A330. It is rarely used in my experience.
The standard dingdong are regular location specific calls which only dingdong at the specific location being called.
The pilots should still say: "Flight attendants prepare for departure" like on all other planes. Chimes aren't normally used signal takeoff in the cabin, although the annoucement can come with a call, which would signal chimes in the cabin.