How do you block your stolen blackberry phone using the serial number?

The IMEI number is the unique identifier for each handset (whether a Blackberry or any other handset) Every network has the ability to block this number thus rendering the handset useless. Unlike a blocked SIM card, the IMEI number is blocked by the network, rather than the individual handset, and once blocked, this renders the handset useless - changing the SIM will have no effect !