A telecommunications system is disclosed including a host telecommunications network (A) having a radio access network (6) and a virtual telecommunications network (C) with which a telecommunications device (3) is registered and operable to communicate with a telecommunications device (3) using the radio access network (6) of the host telecommunications network (A). Network (C) is therefore an MVNO. The network (C) includes means for generating an identifier for indicating that the telecommunications device is registered with the network (C) and for adding that identifier to communications related to the telecommunications device (3) transmitted to elements of the host telecommunications network (A). This identifier is a virtual network identifier (VNID), and can be used by the elements of the network (A) to provide differentiated services to subscribers of the network (C).