Evidentiary value of recorded calls

State the facts of the case. Once a case been allocated to CBI then  they will start the investigation  they can collect the details from all sorts. 

CBI may or may not register FIR as it depends upon the information alleged.

However, CBI shall / can inquire (but not investigate) to determine whether there is some cognizable offence is made out in the information or not .

Academic questions may be put to your professor / guide / tutor as this platform is meant to oblige needy litigants.

Any investigation commences after receiving information or complaint and basing on solid evidence FIR can be registered, where the accused is in a powerful position to manage police or other agencies.  There is a well laid down procedure for tracking the calls and a higher authority that is specifically empowered to request service providers or direct cyber cell can only take a decision basing on facts provided to him in writing explaining the allegations and need for such tracking to avoid further crimes. Depending on solid evidence the FIR will be registered.

These allegations are new in India, right from emergency time till date, there are accusations against political parties in rule that the opposition leaders calls are being recorded and I am not even aware of single case where court pronounced such verdict against CBI/Police.  There can not be smoke without fire.

The CBI can track the telephone  of suspected people on getting the information about the commission of an offence even without a FIR is registered.

This may be termed as preliminary investigation to trap the accused.

Getting the details of the person through his telephone may be a vital information to register the case against the absconding accused. 

This is not uncommon.