Mobile Number Portability is finally here!
Q. What is MNP?
MNP allows users to retain their mobile telephone numbers even if they switch operators. Once the switching begins, it will also force telecom providers to improve the quality of their services.

Q. How can I avail MNP?
Follow 10 simple steps.

Step 1: Send an SMS to 1900 in this format: PORT
eg. PORT 9000000000

Step 2: You receive an SMS that contains a unique porting code
Step 3: SMS this unique code to your preferred operator.
(Note: This code is valid only for a few days. You will have to re-apply if it expires)
 (Or) goto the nearest Customer service center (or Retailers) of N/W you want to shift. (for ex, if you are shifting from Airtel to Uninor, Goto Uninor Customer Center).
Step 4: Fill the Form, submit your identity proof, address proof, and photograph and pay Rs. 19. In the form You have to mention UPC Code ( From Step 2).
Step 5: They will give a new Empty SIM.

Mobile Number Portability is finally here!
Step 6: Your current operator will contact your new operator. If there are no dues, you will be granted approval
Step 7: You will get an SMS stating the time and date that porting will take place
(Remember, the rulebook says the process should be completed within 7 working days of applying except in J&K, Assam and North-east areas, where it will take 15 working days)
Step 8: After porting is done, await a confirmation SMS from your new operator
(Your phone could be unavailable for about 2 hours when porting occurs)
Step 9:  After this 2hrs the new SIM (From Step 5) will work.
Step 10: Now You are in the new network with old number.


Q. How much would it cost me?
The cost of porting a number to a new operator is only Rs 19.

References: 
http://www.ndtv.com/article/india/mobile-number-portability-at-rs-19-80612