I think I made right decision by taking Idea Corporate plan if Prepaid 3G rates are increased in my circle as well.
After making lots of calculations I concluded that with 28 days pack, we pay for almost 13 months in 1 year, where as same pack in Postpaid we pay for 12 months only (but postpaid has service tax). My pack is extra beneficial because its corporate pack with which I get extra minutes and sms as well.