You can prevent a thief from using your mobile phone subscription just by calling your phone company and telling them you lost your phone. If you have a SIM in your phone, you can also lock your phone. Your phone will require the SIM PIN code regularly to prevent fraudulent use. The SIM will block any service if the PIN is wrongly entered three times. If your phone has a SIM, you can also prevent the thief from using your stolen phone with his own SIM. To do this though you need to know your phone’s unique identification number, called the IMEI (International Mobile Equipment Identity). If you can also give this number to your phone company, they can block the handset from being used with a different SIM. In many cases, you can obtain your handset's IMEI by entering *#06# on your handset, but your phone may be different. Check with your manufacturer or user's manual. Note the IMEI and keep it in a safe place. If your telephone is stolen, notify your service provider and give them both your mobile phone number and IMEI number.