There are numerous hacks, tricks and exploits to bypass various kinds of limits imposed on mobile data usage by cellphone carriers. No matter how much carriers try to block them, users always find new ways and proxies to bypass them and access mobile data on there cellphones for free.

Airtel and Google have now collaborated to offer free mobile internet access to Google service on cellphones. Suitably named, Airtel Free Zone powered by Google allows users on Airtel network to use Google+, Gmail and Google Search without incurring data charges and even without an activated data plan. Any internet enabled phone can be used to access Airtel Freezone services, only phone's default browser should be used with Opera Mini as the only third-party web-browser supported.

As for the limitations :
1). The free-ride is available upto a fair usage cap of 1 GB per month.
2). Navigation to first page of a website linked from the Freezone search result page is provided free, but further deeper navigation to website would incur data charges however before you are charged, you will see a warning page with the option to sign up for a data plan if you want.
3). Clicking on any pictures and downloading attachments will also incur data charges after warning and opt-in.