What Is a SIM Card?

SIM cards are essential components in GSM cell phones. Each individual SIM card is unique and identifies a specific owner and phone number. This identification process is necessary to connect the phone to a particular cellular network, and most cards cannot connect to any other carrier networks. Without SIM cards, phones cannot make or receive calls, although they can sometimes access data over wireless Internet connections. For complete functionality, users have to purchase, activate, and install SIM cards into their GSM phone.

What Is a Phone Card?

Phone cards consist of prepaid airtime cards and calling cards. Airtime cards add more calling and data minutes to a prepaid phone user's account. These cards allow users to make phone calls and send texts and emails on different types of phones. Calling cards allow callers to access landlines to make calls within a specific country or internationally.

Is a Different SIM Card Necessary to Use a Phone Overseas?

In some cases, cell phone users must purchase SIM cards from international carriers to make phone calls with their cell phones while overseas. It is best to check with an existing cellular provider to ensure a phone's functionality while traveling abroad.