A method, using a mobile device, of providing a mobile device user access to a network other than the device user's home network, wherein the mobile device has associated therewith a device identifier, comprising:
- in association with a given request, providing an identifier having a first part and a second part, the first part comprising a data string from which an identity of the device user's home network operator can be ascertained, the second part comprising a data string from which a permitted entity can determine an identifier associated with the mobile device;
- and
- using the identifier to determine whether to permit the mobile device user access to the network.