"there is no information avaiable for this on internet or in any book"

Well, quite possibly there's nothing that says specifically how to design a 8 Lines Intercom using At89c52, MT8816 , no trunck line involved , only extension to extension talk and only Pulse Dialing - it is highly unlikely that you will ever find a complete solution to your precise requirements "on a plate" just waiting for you on the internet!

However, the necessary principles can easily be found; eg, pulse dialling (aka "Loop Disconnect") is simply a matter of pulse detection & counting.

Don't forget that all this stuff was being done early last century without the aid of any electronics at all - so it should be a doddle for any microcontroller... ;-)
http://www.antronics.co.uk/history/London_Automatic_Phone_System/