Call blocking is one facility that telecom service providers claim is only for the chosen few, for instance the celebrities. Not withstanding its niche appeal, service providers in the country are in various stages of implementing the technology.

GSM service provider Vodafone Essar became the prime mover in introducing a call filtering service for its users, while BPL Mobile is in advanced stages of installing it. Other players like Mahanagar Telecom Nigam Ltd, Bharat Sanchar Nigam Ltd and Aircel are among others contemplating introducing the technology.

According to Vodafone Essar Director (marketing & new business) Harit Nagpal, "We received a lot of calls from subscribers asking if calls from certain numbers could be blocked, as these were harassing calls. These are not telemarketing calls, but calls made by people who know the user, in most cases film stars and cricketers."

Even though the Telecom Regulatory Authority of India has launched its Do Not Disturb Registry, this does not protect users from unscrupulous elements. This is when Vodafone Essar rolled out the service to protect its customers, he added.

The benefit of this service is that it can be activated on a normal cellphone. It is also available to both post- and pre-paid subscribers. The company charges a fee of Rs 99 per month.

Mirroring the sentiment, BPL Chief Executive Officer S Subramaniam said: "There were complaints from many users of repeated harassing calls from certain numbers. Even though this issue was raised only by a fraction of our users, we decided to install a suite to block rogue callers".

The Mumbai-based GSM service provider is close to launching the service and has already developed a suite for this.

The service works much like the spam blocking facility on e-mails, but only for calls. A user can list certain numbers with the operator from which he does not want to receive calls, and calls from these numbers would be blocked. Around 10-15 numbers can be blocked, while the caller will get a "busy tone or a recorded message".

Reliance Communications [Get Quote] uses a different method to block persistent calls that create problems for its customers. The company has introduced spam controlling software in most of its handsets that can block up to 10 prior listed numbers.

SP Shukla, president (personal business), Reliance Communications, said: "A majority of our handsets have spam call blocking facility, while the remaining would be taken care of by the telecom ministry's DND registry. The service being on the handset, we don't charge additional fee".