Matrix is notorious for their hidden charges and substandard after sales service. While selling the connections , they will appear to be profesional. They do are very professional in selling. You will be impresssed with the promptness and offers with explanations. But majority of the users regret once they see the bills.

Few suggestions

Buy a local SIM , it can be purchased at most of airports, your passport /VISA is enough . This will be the cheapest option

If at all you have to depend on Matrix , do not give your credit card details to them while taking SIM card.

Insist on SIM card without GPRS.
They usually give SIMs with GPRS pre activated. This is very tricky since data service is extremely expensive outside India. Even if you do not use it , many data transactions will be happening with the handset if data is activated. All these will be charged and the bill will be outragoues. Matrix will not give any explanations , they will charge you. The customer care is just not good; getting any response is frustrating