Thanks all,
but i can provide more website than this on such subject and the PBX schematic site... i have gone through that 100 times.. now if any one who can just read the text carefully he will notice that there is nothing in it.. its all rubbish....
And if any one who understand this website just answer 1 question and help me in solving it , let see who can understaand from the links mentioned by Lee Cross and Charles Bannister...

1) You have two telephone sets pulse dailing they are not connected to any external line.

2) Now you connect these two sets by using a 18 Volts DC supply and a 330 Ohms Resistor (1/4 watts) inj series.

3) Now when both telephone sets are in off-hook position conservation can take place and if any of the set is not no current flow and no conversation occurs.

4) Now let say that i want to bring a controller 8051 in between these two telephone sets.

5) Now when ever any of two telephone set goes off-hook state , the user hears a Dial Tone in his telephone set, and then if he dails a digit "1" , it gets connected with other telephone set.

6) Now there is no ringer circuit involved , its just an experiment kind of thing...

7) I have seen one of the post on this website about TONE , and i have written a program for 400Hz frequency and related delay and then i connected p2.0 with a C828 Transistor Base , transistor's collector is connected with positive of 18 volts supply , the negative of supply is connected with Telephone No.1 and transistor's emitter is connected to 330 Ohms resistor who;s other end is connected to Telephone No.2.

But i did not got any TONE in any telephone set...

Now the objective is and any one can suggest any thing any component and software writing technique:-

Telephone User 1

Telephone User 2

Now when user 1 picks up the Hand set of his telephone set he hears a Dial Tone, then he press digit "2" ( Pulse dailing) , user "1" starts to hear a similar tone which we hear when ring is going on other telephone set...although hear the Telephone "2" does not ring...at this stage when user "2" picks up his handset the tone from telephone user "1" set is gone and "1" and "2" can do conversation.. similar process goes for set "2" but he has dail "1" in order to get connected with telephone set "1".

Now please suggest some way of doing this.