On your iphone go to settings->general->network.
Under cellular data network,go to Internet tethering and enter the
APN as 'bsnlnet' without quotes.
Then turn on the GPRS/EDGE or 3G on your iphone 4, you will get a personal hotspot option,turn it on,it will ask for bluetooth,USB or wifi for connectivity,give as per your need and surf.....
Enjoy tethering........