Came across a site called YourBillBuddy.com, which seeks to help you find if your service provider has indeed offered you the best possible mobile talk plan based on your requirements.
You need to register with your mail id, following which a password is sent to you. You can then either upload your phone bill (as a pdf or html file, less than 2 MB) or manually enter the requisite bill figures, after which it analyses the content and checks for comparable plans being offered by other companies. If it finds one, it suggests a new plan or vendor.
This is presently a free service, and can accept both postpaid and prepaid bill details of almost all the major players across all regions.
Though this is a pretty good idea, I feel it will become even more useful once the Government actually implements number portability, allowing people to switch operators. Till then, users are likely to continue to hang on to their cellphone numbers and use whatever tariff plan their vendor dishes out.