Mobile Number Portability (MNP) was implemented in 2011 and now a quite commonly used process by people who want to take their mobile number along when they switch mobile operators.
What to do?
First you need a UPC code.
Inorder to get UPC code SMS
PORT <mobilenumber> to 1900
For example PORT 1234567890 to 1900
You can also call to 1900
Visit nearest retailer with UPC Code
Submit application form,address proof,photo, aadhar copy
You will get your new operator SIM.
It will be activated within 7 days.