Few years back if we need to move to new service provider you have to leave your number and take new connection with new number. After that Mobile Number portability introduced (MNP) that is change to any service provider without changing the number.
This service has limitations too that is if you move from one state to another you cannot port your number to another state mobile service provider so you have to take new connection and new number there.
Now TRAI mentioned that MNP for customers should be allowed in whole India that is Move to Any network Anywhere in India without changing your Number. TRAI has given 6 months for the Mobile Service Providers to introduced this new service so the customer will get full freedom to change the service provider any where in India.
TRAI also mentioned that service provider must inform and educate the customers to use the country code '+91' while calling from mobile phones this can avoid the confusion of STD and Local numbers.