Neither mobile data nor an internet connection is required to call the phone number (000 0800 9191000) which is available to answer questions 24/7. The phone line is offered in both English and Hindi, and there's no charges for the call or for using the service.
The examples given by Google for use cases of the service include asking "for everything from sports scores, traffic conditions and weather forecasts to help with homework". The idea is to provide some of the convenience of information available through a Google search to people who wouldn't otherwise be able to access it.
India has been the target of a recent push by Google, including rolling out new features in the country, introducing tools like a flood prediction system and debuting educational initiatives like a learn to read app. The company estimates that 460 million people in India use the internet, leaving more than half the population of 1.3 billion without internet access.