Unlike some network carriers, UK carrier 02 does not require you to activate your Pay-As-You-Go Subscriber Identity Modules (SIM Card) as it comes pre-activated when you buy it. However, it's worth registering it so that you can take advantage of special packages geared to your usage requirements that may save you money. Examples include an unlimited free text bundle. Once you've registered the SIM card, you can also top it off online with a bank card and see recent activity.
Insert the SIM card into an unlocked or 02 Global System for Mobile Communications (GSM) cellular mobile phone handset.
Turn on the mobile phone.
Browse to the 02 website (see Resources). Enter the phone number associated with the SIM card into the text box on the website. Press the "Continue" button.
Monitor the mobile phone for a text message. 02 will send you a message with a special code. Enter that code on the current web page.
Follow the prompts to enter your details. The website will ask for various pieces of information. On conclusion of the registering process, take a look at some of the calling packages and associate an appropriate calling package with your account.