AFAIK, only Vodafone and Airtel are servicing the iPhone. Is that right?

Vodafone:

http://vodafone.in/newusers/whyvodaf...s.aspx?cid=mum

5p/10Kb

Airtel:

http://www.airtel.in/iphone3g/iphonedataplan.html

30p/50Kb (6p/10Kb to compare to Vodafone)

Those are only the data plans, calling rates will be separate.

Presumably you would do a prepaid plan instead of signing up for postpaid (which I think would involve more paperwork), but it's hardly cheap.

Assuming you use just 200 MB (200 MB*1024Kb/MB = 204,800 Kb)

That's 1024 INR with Vodafone and 1229 INR with Airtel.

It's fine if you use it just for e-mails and basic web browsing obviously but not really economical to tether with your notebook for videos, songs, etc.

It is possible to sign up for a postpaid plan, but make sure you cancel and pay off the bill on time. Also, they can potentially claim you used more data than allowed (even though you didn't). I had this experience with Airtel when I signed up for a wireless aircard and then tried to cancel it at the end of my trip.