Need suggestion for call conferencing

Hi All,
I just want to know that if conversation is going between two numbers. Then, is it possible that the third number can hear the conversation of the first two number without any intimation to both the numbers. i.e
Suppose an agent and end user are talking to each other, but project manager of the agent want to listen the conversation of the end user and agent without intimating them that he is listening the conversation. Is it possible ? if yes then please provide some information how to do that, if not then is there any way to solve the problem to some extent.

Please suggest.
Thanks

This is the wrong forum for Support questions.

core show application chanspy

Please note that this is illegal in some countries, in particular France, where the parties need to have a warning tone when this starts to happen.