A method of activation of a SIM in a mobile device includes sending an authentication request 30 from the SIM 4 in a mobile device 2 to an HLR 22 corresponding to the mobile network operator of the SIM 4. When the HLR 22 does not contain a record that the SIM is activated, not merely does the HLR 22 return a rejection of the authentication request but additionally a provisioning request 32 to provisioning server 24 is automatically made. The provisioning server 24 then, in response to the provisioning request, updates the HLR so that the HLR does contain a record 23 that the SIM is activated such that subsequent authentication requests from the SIM are not rejected by the HLR. In this way, the SIM is not activated before activation needed. This is of particular utility where the SIM is installed by the manufacturer in M2M apparatus.