If your trips to India are semi-regular (like mine are) it might be best to get a post-paid SIM card. IIRC a few years ago, MTNL/BSNL as well as AirTel and Vodafone had a "no monthly rental, lifetime validation" scheme for postpaid accounts.

I've got an MTNL SIM card that I pop into my mobile before landing in BOM and the phone is good to go. Added benefit of all my contacts in India having my local number, which doesn't change from trip to trip