This number is unique to your handset. Write it down and keep it somewhere safe. If your phone is stolen, you can phone your service provider and give them this code. They will then be able to block your handset so even if the thief changes the SIM card, your phone will be totally useless. You probably won't get your phone back, but at least you know that whoever stole it can't use/sell it either. If everybody did this, there would be no point in people stealing mobile phones.
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