I've been using this since last year.

I use this for UBA
*919*Amount# to recharge your phone line. To top up for someone, dial *919*MobileNumber*Amount#

For the sake of ur credit, don't use bank or quickteller to load ur phone, the money u load from them runs twice as fast than when u recharge with a prepaid recharge card. If u think this to be a joke, try it and observe how fast ur credit runs when u r on calls, u will be very shocked.
I loaded up to 1000 on 3 different occasions, but I never got 30mins worth of call out of it on each occasion.