Hi Krishnan,
This restriction is set by using Partitions and Calling Search Spaces in CCM. You will end up setting up a Calling Search Space (maybe called RestrictInt) that does not have access to place these type of calls. Then you assign this CSS against the extensions that you want to restrict. Have a look;
A partition comprises a logical grouping of directory numbers (DNs) and route patterns with similar reachability characteristics. Devices that are typically placed in partitions include DNs and route patterns. These entities associate with DNs that users dial. For simplicity, partition names usually reflect their characteristics, such as "NYLongDistancePT," "NY911PT," and so on.
A calling search space comprises an ordered list of partitions that users can look at before users are allowed to place a call. Calling search spaces determine the partitions that calling devices, including IP phones, soft phones, and gateways, can search when attempting to complete a call.
When a calling search space is assigned to a device, the list of partitions in the calling search space comprises only the partitions that the device is allowed to reach. All other DNs that are in partitions not in the device calling search space receive a busy signal.
Partitions and calling search spaces address three specific problems:
Routing by geographical location
Routing by tenant
Routing by class of user
Partitions and calling search spaces provide a way to segregate the global dialable address space. The global dialable address space comprises the complete set of dialing patterns to which Cisco CallManager can respond.
From this good doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00803edaab.html#wp10870
Hope this helps!
Rob
