A Business Process Outsourcing (BPO) organisation is
responsible for performing a process or a part of a process
of another business organisation; outsourcing is done to
save on costs or gain in productivity.

A call centre performs that part of a client's business
which involves handling telephone calls. A call centre, for
example, might handle customer complaints coming in over a
telephone.

Thus, a call centre can be considered a BPO organisation.
The converse is, however, not true because there exist BPO
organisations, such as medical transcription agencies, which
handle their business through websites, and do not process
any telephone calls on behalf of their clients.

BPO is a process of hiring another company who will work on 
behalf of you.BPO always work as an intermediate between 
the parent company and client company.

where as call centre is asmall organisation which helps the 
various kinds of customer to short out their problems.call 
centre is a part of BPO.

call centre is a part of bpo