Method for serving visitor subscribers in a mobile communication system

A method for serving visitor subscribers in a mobile communication system, the method comprising the following steps, performed by a virtual visitor subsystem, VSS, included in the mobile communication system:

• detecting a roaming event on an MSISDN of a mobile station, MS, operating in the mobile communication system,
• determining a mobile network operator in the mobile communication system, having an HPLMN which covers a geographic area of the MS, to be a visitor mobile network operator of the MS,
• receiving a visitor IMSI from the visitor mobile network operator,
• assigning the visitor IMSI to the MSISDN of the MS,
• transmitting the visitor IMSI to the MS,
• intercepting an authentication initiation towards the visitor mobile network operator,
• authenticating the MS towards a home mobile network operator of the MS, and
• activating a visitor subscription identified by the visitor IMSI based on an authentication response received from the home mobile network operator.
• wherein the step of intercepting authentication initiation towards the visitor mobile network operator includes:
• intercepting by the VSS, an authentication request, and forwarding the authentication request towards the home network operator and the visitor network operator,
• intercepting, by the VSS, an authentication response received from the home network operator and the visitor network operator, and
• transferring, by the VSS, the authentication response from the home network operator towards the VLR requesting the authentication.