If your phone was lost or stolen and you want to report it on the Blacklist you should contact the operator from which the phone was purchased or your local police force. To report may be needed documents confirming the purchase and the IMEI number of the phone.
Phone whose IMEI number will be blacklisted becomes useless. From now on, you can not use it regardless of the country and SIM card.
Do not steal the phone! do not buy stolen phone! and if your phone is stolen, immediately inform the relevant services.
Ream more about Blacklist check