They said a journalist from a TV channel and a senior executive of a leading newspaper group have already been examined by the agency.
Besides, executives of Reliance, Unitech and Tata Motors have also been examined by the agency in connection with its enquiries.
According to the sources, several big names of journalism from print and electronic media and corporate world would soon be called by CBI for gathering information on criminal aspects of those conversations.
The apex court bench headed by Justice G S Singhvi had ordered the CBI to probe 14 issues that were identified by the investigating agency after going through the transcript of the Radia tapes submitted to it by the Income Tax department.
The court has also referred one of the matters to the Chief Vigilance Officer of the department of mines for investigation and another to the Chief Justice of India.
“Radia's conversations reveal deep-rooted malice by private enterprises in connivance with government officials for extraneous purposes,” the Supreme Court had said.
Using strong words, the court had said the telephonic conversations suggest corrupt means being adopted by private parties to extract gains.
