Most Subscriber Identity Modules (SIM cards) used in cellular mobile phone handsets are already activated when you buy them–usually on non-discounted rate plans. If you do need to activate your SIM card, check out the calling packages available at the same time. Even if the SIM card is pre-activated, you may find better rates on the carrier's website. Activating or registering the card online lets you select special packages which can benefit heavy international users or heavy text users, for instance.
Try to use the SIM card. If it doesn't work, you'll have to activate it on the carrier's website. Some carriers, such as Orange in the UK and AT&T in the U.S., require activation.
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Insert the SIM card in the phone.
Browse to the activation website listed on the packaging.
Enter the phone number or SIM card number on the website. The website may ask you for additional details. It may ask you to set up an account before it will let you select a discount package.
Follow the steps on the website and monitor your phone for any text messages. Follow any instructions that come in the text message. Text messaging is often used to get network configuration details to the phone, mainly for Internet functionality and picture messaging.
The SIM card number is printed on the SIM card packaging, on the outside of the box the phone came in, and on the SIM card itself. The phone number will be on the packaging but may not be on the SIM card.