Abhilash,
You can configure the dialling privilege at user or station levels.
At user level under user container or role or workgroup Security tab/Access Control Phone number classification.
At station level, In station container/Access Control.
To understand whihc one you need if you do not wish a=to give all access simulate the number in Simulate call in IA/System Configuration/Phone Number/Regional Dial Plan
Hope this will help.