A cell phone's SIM (subscriber identity module) card is designed to hold basic information, including contact lists, text messages and sometimes calendar entries. When it's time to sell or donate your cell phone or if you just want to wipe your card clean, you'll have to reformat it, which means you will delete the card's memory and start fresh.
Find the data reset commands for your specific cell phone model by using the Cell Phone Data Eraser on the Wireless Recycling website at recellular.com (or a similar service). These types of websites issue instructions for just about all phone models for free or a fee. Enter the cell phone model, register with the service and retrieve the PDF file that is sent to your email account. You will find reset instructions for your cell phone model in this PDF file.
Follow the unique instructions for your cell phone. The code, which is found in the PDF file, is a series of keystrokes specific to that cell phone model and it will reformat the SIM card.
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Turn off the cell phone, then restart it. Go to your address book and choose the option to display SIM contacts. If your address book is clear, then you know that your SIM card has been properly reformatted. Also, check your organizer and other features to make sure they are cleared as well.