A Three 1GB Data Sim, or Subscriber Identity Module, is a card located inside many mobile phones and other mobile devices. These cards serve a couple primary purposes. For one, they store data, such as the phone owner's contact list. When you have a SIM and you get a new mobile phone, therefore, you don't have to start compiling a new contact list from scratch. Instead, all you have to do is remove your card before getting rid of your old phone, and insert that into the new phone. These also let people avoid roaming charges during trips abroad. When you travel overseas, you can purchase a new SIM card and put it in your phone. This foreign SIM will let you make calls on local networks at local prices.
There are some important matters to keep in mind when it comes to cards. First, realize that not every mobile phone can hold a SIM. Only unlocked Global System for Mobile Communications (GSM) phones have slots. Second, be careful not to lose your regular card while it's out of your mobile device. Also, whenever you have a different card in your phone, you're given a new phone number. That new number is assigned when you purchase the card, and people who try to call you at your usual number won't be able to reach you. As soon as you put your old SIM back in your phone, you get your old number back.
The first to hit the marketplace was about the size of a credit card. Then that card shrunk, and this new, so-called "mini SIM" enjoyed years of popularity. Then the mini SIM got even smaller, and it became the "micro SIM card." Micro are sometimes referred to as 3FF cards. "3FF" stands for "third form factor," a reference to the fact that it's the third version of the SIM. The creation of the 3FF card was necessary because some new wireless devices were so small, even Mini SIMs were too large for them.
Apple has put micro cards into some models of its popular iPad tablet. Not every iPad model uses a 3FF card, but the original 3G iPad, the iPad 2 3G, and the iPad 3 with cellular data, among others, can all accommodate an iPad SIM card. Apple has asserted that micro cards offer stronger security measures for users' data. These hold more data as well. That is, where the original SIM could only store names and phone numbers, this latest iteration of the card can store email addresses and other kinds of information.
Expect to see an even smaller SIM, the "Nano SIM," grow in popularity. In fact, some iPad mini models are beginning to use this fourth version of the SIM card already.