PUNE: Search giant Google has started rolling out ' free SMS ' for its free email service Gmail and paid email service Google Apps customers in India. The service allows users to send SMSes to mobile phones from chat windows. Users have to add mobile numbers of their contacts in the email address book and they are set.The service starts with 50 SMS credits for each user, every sent SMS costing one credit. Every reply received adds on 5 credits subject to the maximum level being 50 SMS at any given time. There is no official statement from Google on the launch of this service, however the service has gone live this evening in the chat windows of many users.Google is rolling out the service in partnership with cellular operators, which means they would share revenue with Google out of SMSes users on their network send. It specifies a way to buy more SMS credits. "You can always send an SMS to your own phone, and then reply to that message multiple times. Every time you send a reply message, your SMS credit is increased by five. Effectively, you're buying more messages by paying your phone company for these outgoing messages," it writes on its chat help portal.The service currently supports eight cellular operators including Aircel , Idea, Loop Mobile, MTS , Reliance, Tata DoCoMo, Tata Indicom and some circles of Vodafone . BSNL, MTNL and Airtel are not supported yet.The SMSes sent from Gmail chat are delivered to mobile phones while replies from the mobile phone come into the chat window. For the mobile phone user, the reply is charged at local SMS rate as per her/his normal billing plan.If no replies are received to any of the 50 SMSes sent and the credit balance come down to zero, Google says, "...it will increase back up to one 24 hours later. So, you won't ever be locked out of the system."