In India depending on how much mobile usage you have considering your local and std calls and sms there are various plans available in your city or state. Finding out the best talk plan for you to get the most of your money, Change My Network has created a tool which is worth trying out.
This tool takes in the input of your current plan ( postpaid or prepaid ) along with the kind of usage you have ( see snapshot below ) suggests you plans available with other mobile operators. For example I am using Vodafone Prepaid plan and this tool suggested me similar plan in Kolkata which I can opt in.
The main idea of Change My Network is to ease you with change of mobile operator once the Mobile Number Portability (MNP) is introduced in India which was supposed to come this April. It might take 7 days for change of operator and includes a minimal charge of 19 Rs. However this seems to be coming after October but we will have to wait for final confirmations from the TRAI.