Michael ,
sir thanks a lot for your helpful replies..now iam working on to understand your code and will reply as soon as possible

But the Bit High and Low thing....

In our commerical Market i have seen 4 8 lines intercom exchange of different manufacture and i have checked their hardwares properly and all have Active High on Off-Hook...

so there is not one company who is doing this but four company and they are not doing this from now or 1 year back they are doing this for last 8 or 9 years...

so you all mean to say that they are wrong and putting the bit to high and the off hook to low is the correct way...

i will be back with your code...