If you are willing to pay 1200 Rs per month you can get unlimited data usage on your iphone with Airtel sim.
This is not a hack or a trick. You are paying for their highest data card plan and using it.
Here is what happened, I bought a data card from Airtel with unlimited data plan for which they charge 1200 Rs. I bought this with a USB modem so I am not sure if you can get just the sim, I think you can.
Soon after that I got broadband so I didn't need this Airtel connection. But rather than canceling the connection I removed the sim from the USB modem and put it in my iphone. So now I can use unlimited data with an Airtel sim.
I know 1200 Rs per month is pricey but you get very good speeds a lot faster than bsnl. I get speeds of 91 Kbps. I have a photo of the speed test too. The best part is I can use you tube and watch videos do chatting listen to radio now matter where I am. I can even use the same sim for calling too, prices are standard with any other mobiles.
I used it on a 1st generation iphone 2g (jail broken iphone), it should work with the new iphone too. Do comment if this also works on iphone 3G.
In fact I wrote this whole blog post from my iphone using word press app. And Airtel sim to upload it to the blog.
The best thing about using this Airtel sim is that you can use it even when roaming. Do unlimited data anywhere in India.
This would work with others phones too. But if you have not done it yet just get a demo of browsing on iphone and you will not go back to other phones.