now the called party is not getting and kind of notification that some one called .. calling party gets to know that the called party is busy . but called party should get a notification (flash/beep) so that called party should get to know that some one called....

Thats essentially how it should work. If I call you and you are on the phone and only want to handle one call, then the person calling should hear a busy signal and you being on the phone and not wanting another call, should hear nothing. Now if you want to know that someone is calling you, then you need to increase the busy trigger to "2", the person calling is not going to hear a busy signal because if the person accepting the call has the option to know that someone is calling then they should have the option to pick up the call. I guess i dont understand the need for someone calling to hear a busy signal and the person that is on the phone wanting an indication that someone is calling them when they still cant do anything to pick that call up and accept it.

thanks tracy for the nice explanation ...

but what i think of this is say for an example my reception phone is busy with some call and if some senior or boss or some important client called on that number the receptionist should get to know who called and she can put on hold the first call and attent the second call. and if she dont want to entertain the second call then again no one will say its her fault becoz she was busy with call call and calling party will hear busy tone and not the ringing tone. This is how it works on Mobile on INDIA. if this is not possible with cucm not an issue but this is what we call in INDIA a call waiting option where both the parties gets notified about the call & once the called party gets free from the ongoing call he can call back to the number.

check if this is possible

Another option you could play with then is adding each of the people to a "Pickup Group". Within the pickup group there are options that would display who is calling who visually on the phones that are in the pickup group when the call comes in. If the visual method is not enough then you can also enable an audio alert that accompanies the visual alert. This may help you accomplish what you are trying to get.