"You can send SMS messages to your contacts' mobile phones using Gmail Chat ... Google does not charge for using this service," according to information available with Google's website.
The SMS service is available in India and 51 other countries in Asia, Africa and North America.
The feature was activated for Indian users on October 10 and is available for regular Gmail users as well as those on Google Apps.
As per Google's website, this feature is available on all the mobile operators in the country.
The company said in order to send an SMS, users would have to add phone number to their contact list.
Responses to the SMSs would appear as replies in Gmail Chat and conversations will be stored in users' Chat history, like regular chats.
Google initially provides free SMS credit of 50 messages for each user. For every message sent, users' credit woud decrease by one. However, this credit would increase by five every time a user responds to the text message by sending a return message.
In case, the SMS credit limit slashes down to zero, one credit would increase automatically after 24 hours.
Google said users can also 'buy' SMS credit in case of shortage by sending a text message to their own phone and then by replying to that message.
The internet firm has also provided the facilities for those users do not wish to receive any messages on SMS from any Gmail user.
In order to send an SMS from Gmail, on the Gmail Chat interface type the phone number you want to send an SMS to and click Send SMS and then add the recipient's name and country, then click Save. Then write text in the chat window and press Enter.