hmmm, thats a good question:
Looking at the manufacturer website **broken link removed**
I see that the HT2811 IC has been discontinued. Thus Holtek doesn't have the datasheet on this IC any longer.
I see a similar product HT12M which is designed for a transmitter / receiver system. (LOL, I searched under customer service for "Ding Dong", doorbell didn't work for a search). I don't know if this is what you're after, but it is a start, nevertheless.
**broken link removed**
It looks like Holtek has a forum for application questions etc. I didn't want to register, so I didn't check this out. Maybe you want to?
Aside from the IC, it would be possible to create a ding dong sound using a timer and a couple of piezo buzzers, but that would involve some experimenting with different discrete components in order to create the sound that you're looking for.
Maybe someone has a datasheet or something. Sorry Im not much help here.