Department of Telecom has issued (.pdf) a notification stating that long awaited number portability will finally be available by September 20. The main object of number portability is to be able to retain the same number even after switching between different mobile service providers.  

Mobile Number Portability gives a mobile subscriber the leverage of retaining his/her mobile phone number even after switching between networks. As per Department of Telecom - Mobile Number Portability is to be implemented in Delhi, Mumbai, Maharashtra and Gujarat Service areas of Zone I and Zone 2 includes Kolkata, Tamil Nadu, Chennai, Andhra and Karnataka of within six months of award of license by September 20, 2009, and in the rest of the country by March 20, 2010. 

Syniverse Technologies have been licensed for MNP operations in Zone I while MNP Interconnection got licensed for MNP operations in Zone 2.  

TRAI will decide all kinds of mobile number portability tariffs like the transaction fees from customer seeking number change. Also TRAI will try to keep cost of the Mobile Number Portability at reasonable level so as most subscribers are not put off by the charges.