Low-cost calling apps like Ringo are offering service at nearly 90 percent cheaper rates than telecom operators.
Ringo is learnt to have been using Quadrant Televentures' network, a subsidiary of Videocon Telecom, for providing service. The company said it has permit for providing teleconference services and uses it along with other technology to connect calls.
Bharti Airtel Chairman Sunil Mittal had expressed concerns on the service of Ringo in presence of Telecom Minister Ravi Shankar Prasad on December 1, alleging that Ringo is "gaming this system" which will hurt mobile industry.
Mobile operators are already facing challenges in voice business as consumers are switching to messaging apps like Whatsapp that offer free voice calls too.
Moreover, operators have started providing unlimited free calls from landline to any network across the country by charging low monthly fees.
Ringo said its services are legal and are compliant with regulations. The company is working on a "favourable resolution in due course of time", it said.
Regulator, TRAI, said it is examining the issue and would come out soon with suitable action to address the operators' concerns.