The phone will work, as will sms. What people mean is some of the very nice BB features do not work such as push email and BB messenger. Generally it's just a bit annoying to have to work around the limitations.
Lots of the Nokia GPRS apps you've mentioned are probably not available. Google and Yahoo apps are.
For the browser, you will have to use a browser like Opera Mini. Well there is a thread on how to get the BB browser to work, so you could try that. But generally you need a BIS to use the BB browser. Also I know in Thailand the BB browser will work with a basic prepaid AIS sim, but I doubt the Indian carriers will push the service books automatically. But if you're lucky they will for even the basic data plan.
Other than say the Gmail app and Yahoo Go (which is not good on this phone) you'll have to check email via the browser.
Over wifi, it's about the same I think with slightly more things you can do. Long thread on what you can/can't do. Read it somewhat backwards so the more recent stuff is first: http://www.blackberryforums.com/wifi...-can-t-do.html