Advice: Mobile

The gsm system is used in India. The biggest network providers are Hutch and Airtel. If you plan to stay in India for a few weeks or months, I would recommend you to buy a prepaid card. They can be found everywhere. Make sure to have an ID picture and a copy of your passport. Prepaid cards cost Rs200, Rs300, Rs450, Rs600… Rs150 are automatically charged for the incoming calls.

For example, a Rs600 card gives you the right:
-to receive incoming calls during one month. Without limit…
-to send sms and to give calls for a value of Rs450

Source

Sms and calls are quite cheap. Especially within the state in which you bought the card… If you want to reach someone who is in another state, the cost will be a bit higher.

If you plan to travel in another state, don’t forget to activate the roaming option before leaving the state in which you bought the card. It will cost you around Rs50 per month. Once you are in the other state, sms and call rates will be higher and you will also have to pay when you receive calls! Conclusion, try to buy the card in the state in which you plan to spend the most of your time.