In the UK, a stolen phone (if reported) can have its IMEI number used to block and prosecute theives. I imagine almost all phones will have users who will eventually put a SIM card in there and when they do - wham! To be 100% safe, a user will need to unblock (not unlock) the phone. Which requires actually changing the IMEI/Serial number of the device. Not only is this illegal, it's not easy to find people who do this for you. I have my N900 insured under my credit card, and most banks in the UK now provide an upgrade to their current/checking accounts which gives free phone insurance. Vital with something as expensive as the N900 and much cheaper than carriers insurance.