IMEI oops !!
I accept what you say, but if people are not aware the number even exist or don't now what it is then then police cannot make the effort which they do.
This may or may not be correct:-
From internet :- In the case of a theft, an IMEI number can be used to disable a phone so that it can no longer be used on any network. Every (reputable) mobile phone operator subscribes to the IMEI Database, a worldwide blacklist of IMEI numbers that have been reported stolen. Subscribers will not activate a phone with an IMEI number in the blacklist database, preventing thieves from simply taking your phone to another company after your operator disables it on their network.
The IMEI is not a full-proof system; a phone's serial number can be faked, although this requires fairly sophisticated knowledge and equipment. Someone may clone your IMEI number and trick your operator into charging your account for their usage, or your stolen phone may be given a new IMEI number which allows the thief to activate it. However the IMEI system's robustness and universal adoption in the industry means that it works for the vast majority of cases, provided you remember to record your IMEI number ahead of time and react quickly if your phone is stolen.