A network usage control computer implemented method comprising: receiving, at a network operator from a requesting terminal device, a handset identifier of the requesting terminal device seeking to use a mobile network, the handset identifier comprising an International Mobile Equipment Identity "IMEI" number; retrieving (S3, S6), by the network operator from the requesting terminal device, verification information for verifying an identity of an authorised terminal device associated with the handset identifier, the verification information comprising information for verifying the binding between the IMEI and the requesting terminal device, wherein the verification information comprises cryptographic identity information representing a cryptographic identity of the authorised terminal device associated with the Handset identifier; verifying, by the network operator, based on the verification information, whether the requesting terminal device is said authorised terminal device; and controlling (S10, S11), by the network operator, usage of the mobile network by the requesting terminal device in dependence on whether the requesting terminal device is verified as said authorised terminal device, wherein said controlling usage of the network comprises controlling whether the requesting terminal device is allowed to switch from a limited communication mode in which a limited subset of network communication functionality including only emergency calls and the handshaking for the handset identifier and subscriber verification based on retrieval of the verification information is allowed to a full communication mode in which communication functionality other than said limited subset is allowed, in dependence on whether the requesting terminal device is verified as said authorised terminal device. receiving, at a network operator from a requesting terminal device, a handset identifier of the requesting terminal device seeking to use a mobile network, the handset identifier comprising an International Mobile Equipment Identity "IMEI" number; retrieving (S3, S6), by the network operator from the requesting terminal device, verification information for verifying an identity of an authorised terminal device associated with the handset identifier, the verification information comprising information for verifying the binding between the IMEI and the requesting terminal device, wherein the verification information comprises cryptographic identity information representing a cryptographic identity of the authorised terminal device associated with the Handset identifier; verifying, by the network operator, based on the verification information, whether the requesting terminal device is said authorised terminal device; and controlling (S10, S11), by the network operator, usage of the mobile network by the requesting terminal device in dependence on whether the requesting terminal device is verified as said authorised terminal device, wherein said controlling usage of the network comprises controlling whether the requesting terminal device is allowed to switch from a limited communication mode in which a limited subset of network communication functionality including only emergency calls and the handshaking for the handset identifier and subscriber verification based on retrieval of the verification information is allowed to a full communication mode in which communication functionality other than said limited subset is allowed, in dependence on whether the requesting terminal device is verified as said authorised terminal device. wherein said controlling usage of the network comprises controlling whether the requesting terminal device is allowed to switch from a limited communication mode in which a limited subset of network communication functionality including only emergency calls and the handshaking for the handset identifier and subscriber verification based on retrieval of the verification information is allowed to a full communication mode in which communication functionality other than said limited subset is allowed, in dependence on whether the requesting terminal device is verified as said authorised terminal device.