But the system is clearly not working. While 90% of numbers on NDNCR do not receive ad pitch calls, the system is a failure when it comes to keeping out unwanted SMSs.

"The response to NDNCR has been far from satisfactory, with only 50-60 million subscribers (from India's subscriber base of 562 million) opting for this service, with just a 60% success rate," says Trai chairman J.S. Sarma.

He cites two reasons for this: "People are flouting the law and there is lack of awareness of this service."

Lack of awareness can be remedied in time. But flouting of the law means even those who avail of NDNCR are not beyond the reach of irritating ad pitches.

"The fines laid down (for violating NDNCR) are clearly not enough," says Sarma, explaining why telemarketeers flout the law. "We have asked for more punitive powers from DoT."

The department is considering Trai's request, says P.J. Thomas, secretary, DoT.

"Everything is clearly laid down according to the guidelines and has been comprehensively looked into by Trai," says Thomas. "It has undertaken a wider process of consultation and we will consider further recommendations by them."

Currently, the penalty for violating NDNCR is Rs500-1,000 and, ultimately, disconnection. But that is hardly a deterrent for telemarketeers.

Mint contacted a telemarketeer to get an indicative rate, and found a one-time promotional SMS facility to 10 million numbers across India would cost 5 paisa per contact. That adds up to Rs5 lakh as income for the telemarketeer.

But how do telemarketeers manage to evade NDNCR? The answer is easy availability of SIM cards, which can be bought in a personal capacity but used to send bulk messages, and the use of the Internet to send illegal SMSs.

"A lot of the mid-tier call centres flout the regulations given the risk-reward ratio attached to it. The rewards outweigh the penalties," says Alok Shende, principal analyst, Ascentius Consulting, an IT consulting firm.

"All you need is an investment of around Rs2,000 for an Internet connection, a device called an analogue terminal adapter and a software easily available through open source to put these calls through. Then you can make Voice over Internet Protocol (VoIP) calls," he explains, adding that strong penalties are required to curb the menace.

Bijon Misra, chairman, Consumer Education and Advocacy, Delhi, also says authorities should revoke the licences of service providers who are not checking telemarketeers. But service providers in turn point to Trai.

In an email response, Bharti Airtel Ltd, India's biggest mobile phone company by subscribers, said NDNCR hasn't worked "as comprehensively or satisfactorily as desired" and apportioned the blame on two or three "tolerant operators".

"This is reducing the impact and also the spirit of NDNCR, not to mention the general public's assessment of its effectiveness. Trai is aware of these errant/tolerant operators but has not taken any governance or corrective measures on any of these operators," Airtel said.

Mobile service providers Vodafone Essar Ltd and Tata Teleservices Ltd did not respond to queries from Mint.

Trai is now contemplating a "Do Call" structure, which will restrict telemarketeers to advertising with only those users who expressly ask for it.