Hi Gemeni,
Thanks for ur reply,
We have TA-624 system.We connected one KX-T7730 and two other regular phones to TA-624.We also connected TVS-50 voice processing system to TA-624.
I did exactly what you recommended.
From KX-T7730 i have done the following:

1. Lift the handset.
2. Press 7311#
3. We got confirmation tone "CW(CO) ON" in the display.
4. From an outside line, Called main number xxx-xxx-xx90, ext. 101
5. From my cell , called main number xxx-xxx-xx90, ext. 101.
6. We didn't get any call waiting tone in the
xxx-xxx-xx90, ext 101.

Please help.

Thanks,
Evan1