I have done some research, and PHV is not just about charging the nromal battery. The PHV Prius has a much larger battery, and ill on a full charge of 2 hours give you first 20 Km (max speed 100 km/hr) on Battery alone, with no engine!
Therefore its fuel economy will also be much much better, especially if you do smaller journeys and can plug in to charge at home or office when you get there! The cost of charging will be around 3KW for whole charge according to prius owners on various forums, which at current electric prices would be around 40 Rs. Lets see when they come here, but I would love driving most of the time on Electric only, and having a full tank where the needle doesn't go down unless you go out of city!