Dial plan

Hi All,

We have Freepbx hosted in three locations(India and UK).

All are interconnected with IAX trunks. Now i need a dial plan or feature which prevents the following transfer calls.

We have 1XXX extensions on UK and 2XXX extensions on India.If 1XXX calls an extension on 2XXX and 2XXX tranfer the call to an extenal number, that should get prevented.

Please help me on this requirement.