

The network operator is expected to blacklist the IMEI by the law in the operator’s jurisdiction, if asked by owner in case of phone gets stolen or lost.A bill was proposed to Congress by Senator Chuck Schumer in §3186 of the 112th Congress in 2012but has not been approved. In the United States, changing the IMEI of a phone is not illegal.In the United Kingdom, under the Mobile Telephones (Re-Programming) Act, changing the IMEI of a phone, or having any equipment that can change it, is considered an illegal offense under some circumstances.Have a look on How to Dual Boot Multiple ROMs on Android Phone.

So, the phone become useless on that network and sometime on other networks, even if the thief changes the phone’s SIM. Also you can contact the network provider use the IMEI Number to blacklist the phone. Cellular network use the IMEI Number to identify valid device, and can stop a stolen or lost phone from accessing the network.
