The invention relates to a method and system for providing mobile based services for hotel PBX having an external number assigned which includes the steps of providing each hotel room which provides the mobile based service with at least one mobile station comprising a SIM, each SIM storing a different IMSI number; assigning a VPN to the hotel; assigning each IMSI number of each mobile station to a different MSISDN that can only be used internally in the MNO network and that cannot be dialed from other telephones; and assigning each MSISDN to a different extension number that can be used as a room extension number and that corresponds to the VPN number of the VPN of the hotel. The invention is advantageous in that it solves problems of prior art systems by making use of a mobile PBX, so that every hotel will have its own VPN numbers that can be used as room extensions.