Data cards are nothing but they are the cards which provide you data usage to use internet , it is like passport & visa required for travelling for abroad .

When you buy a data card it means that suppose you bought 1GB data of 4G or 3G it means that for a particular time you will be able to send & receive data for throughout its validity .

When you request a site to open it , you send data & when site got opened data got received .

Data cards are available at your nearer retail store you can buy it there & According to your area you can choose company which network is good
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