I was told for the first 3-4 days it wouldn't cross 2mbps today is the 2nd lemme wait for another 2 and see if i get 4mbps , and i hope mine is unlimited too xD
Iam also from chennai i asked airtel to upgrade my plan to 4mbps they told me its not possible for my line at present 4mbps is offered to lines which are close to exchange pillars ,They also said they can give that plan but i would be getting max 2mbps speed and not 4mbps and for full 4mbps they need to upgrade their network ,so be cautious in getting 4mbps plan