As someone who worked for a VoIP CLEC, I can tell tell you it's possible but not garenteed.
First, your friend will want to open case with the local police department (ie they must agree to proceed with prosicution if the person(s) is/are found due to the amount of effert involved).
Second they need to submit the police case number along with the assigned officers name a contact info to their own phone service provider and request a "trap". If the calls are happening more at a certain time of day, it'll best to let them know.
Their localprovider can let them onow any additional steps needed.
Please note that even if the trap picks up a DID (phone number) for the calls, the CNAM info caller ID) can be spoofed.