If you still get unsolicited calls and SMS messages from telemarketers, we thought we’d take the time to provide the exact steps to block these unwanted calls. Having said that, please note that not all companies that make unsolicited calls or send unsolicited SMS messages have registered as telemarketers with the Telecom Regulatory Authority of India. If they make calls using your phone number obtained through other sources (apart from your mobile service provider), there is not much you can do other than to drag the party into court for telemarketing without registration. Even then, we’re not sure how consumer laws in our country apply to such situations. Anyway, as they say, something is better than nothing, and so, following the steps outlined here (if you wish) should block registered telemarketers from disturbing your peace.
(As per TRAI’s guidelines, this applies to landline and mobile numbers)

1. Call or send an SMS to 1909 (toll free) to register.
2. Select the Fully Blocked or the Partially Blocked categories. Via SMS, you would need to SMS START 0 to register in the fully blocked category. For partially blocking telemarketers (based on seven categories: Banking/Insurance/Financial Products/Credit Cards-1, Real Estate-2, Education-3, Health-4, Consumer goods and automobiles-5, Communication/Broadcasting/Entertainment/IT-6, Tourism-7), you would need to SMS START 1,4,5 if you wish to continue to receive calls and SMS from telemarketers in the categories 1,4,5 – calls and SMS from telemarketers in all other categories would be blocked.
3. On successful registration, a Unique Registration Number would be sent to your phone within 24 hours.
4. If all goes well, within 7 days, your request would be completely activated. You can check the status using the Customer Registration Status link.
5. If unsolicited calls or SMS is received even after successful registration of your request within 7 days, you have the option to log a complaint with your service provider by calling or sending and SMS message to the same 1909 number within 3 days of the unsolicited call/SMS. Via SMS, the complaint would need to be sent as follows: COMP TEL NO XXXXXXXXXX;dd/mm/yy;Time in hh:mm; short description of Unsolicited Commercial Communication, where XXXXXXXXXX is the phone number or the header of the unsolicited call/text.
6. If such a complaint is registered with your service provider, it is the provider’s duty to take action and inform you within 7 days of lodging the complaint. You can check the status of the complaint at the UCC Complaint Registration Status link.

Also, all such commercial calls from telemarketers have to be performed between 9 am and 9 pm. The original document with the guidelines laid out by TRAI is available at the source link below.
Source: TRAI NCCP