Essentially, every mobile device can be in one of three states - white (it's OK), grey (it's dodgy in some way, but not necessarily lost or stolen, it could be faulty) and black (it's been lost or stolen).
Mobile networks (in the UK at least) maintain a record of the black or grey handsets using an EIR and sync their database with the Central EIR (which used to be in Dublin, not sure where it is now). By default, all devices are assumed to be white, or the database would need to store every device in use.
When you turn the phone on, the network performs a checkIMEI against their database and if the handset is black listed, the network won't allow the phone to location update.
Obviously, the EIR does not generate any revenue for a network, so not all of them choose to operate one, as it's an overhead (maintenance support, etc).
In the UK, it is illegal to change the IMEI of a device, as this would allow you to circumvent a black listed phone. Poorer countries will probably not have an EIR of their own (due to cost) and so lost and stolen phones often find their way there to be used.
Mobile networks (in the UK at least) maintain a record of the black or grey handsets using an EIR and sync their database with the Central EIR (which used to be in Dublin, not sure where it is now). By default, all devices are assumed to be white, or the database would need to store every device in use.
When you turn the phone on, the network performs a checkIMEI against their database and if the handset is black listed, the network won't allow the phone to location update.
Obviously, the EIR does not generate any revenue for a network, so not all of them choose to operate one, as it's an overhead (maintenance support, etc).
In the UK, it is illegal to change the IMEI of a device, as this would allow you to circumvent a black listed phone. Poorer countries will probably not have an EIR of their own (due to cost) and so lost and stolen phones often find their way there to be used.
