Now you can block commercial communications…unwanted SMSs….

Customers/ Subcriber SMS to 1909 (toll free) and can register in either of the two categories.
Fully Blocked Category- stoppage of all commercial Calls/SMS 
For registering option using SMS, for ‘fully blocked category’, write “START 0” and send it to 1909
Partially Blocked Category- stoppage of all commercial Calls/SMS except SMS from one of the opted preferences. For ‘partially blocked category’, send SMS ‘START’ with one or multiple options from the list of seven categories.
1. Banking/Insurance/Financial products/Credit cards, 
2. Real Estate, 
3. Education, 
4. Health, 
5. Consumer goods and automobiles,
6. Communication/Broadcasting/Entertainment/IT, 
7. Tourism and Leisure.

For example: To receive messages relating to only Health products, then send SMS “START 4” to 1909. Similarly, for receiving messages relating to Real Estate and Education, send SMS “START 2,3” to 1909.
On successful registration, customer will receive an SMS confirming exercised options and a Unique Registration Number within 24 hrs. The registration will be effective within 7 days of placing the request with the service provider. The customers can check the status of their registration by clicking on “Customer Registration Status”.
Customer can also change the preferences after 7 days of registration or the last change of preference.
If customer receives UCC even after 7 days of registration, he can register a complaint with his service provider within 3 days of receipt of such UCC by dialing or sending SMS to 1909. Customers will have to provide the telephone number or header of the message from where the call or message has been received along with the date and time.
For complaint through SMS, customer has to send SMS COMP TEL NO XXXXXXXXXX, dd/mm/yy, Time hh:mm to 1909. Where XXXXXXXXXX – is the telephone number or header of the SMS, from which the UCC has originated.
Service Provider will take action on complaint and inform the complainant within 7 days of lodging of complaint. Customers may check registration status of his complaint through the link “UCC Complaint Registration Status”.
Customers not registered with NCPR can also identify the commercial calls because they will all come from numbers starting with ‘140’. This is a series specially earmarked for telemarketers.
Also, in order to control the possibility of SMS packages (those allow a very large number of SMS per day) to be used by the telemarketers for sending large number of SMSs from a normal telephone number, a limit of 100 SMS per day per SIM has been laid down under these regulations except on blackout days.
Further, all commercial calls or SMS except the transactional SMSs will be sent to the customers only between 9 AM and 9 PM.

DE-REGISTRATION OF PREFERENCE THROUGH SMS
Send SMS “STOP” to 1909.
Source of information