I recently took a matrix card for an International travel of 5 days, and used the card only for calling for few minutes ( 5 minutes daily). Got shocked to find bill of 4500 on coming back! The billing format was not disclosed at time of taking card, the rental per day was not mentioned.
Most importantly, they block 5000 rupees beforehand, so u cant complain about SMSes u haven’t sent, they can directly debit the amount from ur credit card. Dont use this Matrix services..they are not at all clear from start, they gave the tariff in cents/sec, charged in minutes (rounding off each call to minute!), and added rental to day 0 when I was still in India!