Method for a Mobile Network Operator, MNO, to provide mobile based services for a hotel PBX, the hotel PBX having an external number (MainNum H) assigned, comprising: - providing each hotel room which provides the mobile based service with at least one mobile station (1a, 1b') comprising a SIM, each SIM storing a different IMSI number; - assigning a VPN, VPN H, to the hotel; - assigning each IMSI number of each mobile station (1a, 1b') to a different MSISDN (MSISDN A, MSISDN B) that can only be used internally in the MNO network and that cannot be dialed from other telephones; - assigning each MSISDN (MSISDN A, MSISDN B) to a different extension umber (Ext A, Ext B) that can be used as a room extension number and that corresponds to the VPN number of the VPN, VPN H, of the hotel; - for each call originated from a calling mobile station (1 a) of the hotel: - checking if the call is aimed to a called party belonging to the hotel VPN, VPN H " and in that case replacing the calling party number with the extension number (Ext A) assigned to the calling mobile station; - if the call is aimed to a called party not belonging to the hotel VPN, VPN H " replacing the calling party number with the external number (MainNum H) of the hotel PBX; - for each mobile terminated call aimed to a called mobile station of the hotel: - obtaining the extension number (Ext B) corresponding to the called mobile station of the hotel; - obtaining the MSISDN (MSISDN B) associated to said extension number (Ext B); - redirect the call through the mobile operator network to said MSISDN (MSISDN B) of the called mobile station. - providing each hotel room which provides the mobile based service with at least one mobile station (1a, 1b') comprising a SIM, each SIM storing a different IMSI number; - assigning a VPN, VPN H, to the hotel; - assigning each IMSI number of each mobile station (1a, 1b') to a different MSISDN (MSISDN A, MSISDN B) that can only be used internally in the MNO network and that cannot be dialed from other telephones; - assigning each MSISDN (MSISDN A, MSISDN B) to a different extension umber (Ext A, Ext B) that can be used as a room extension number and that corresponds to the VPN number of the VPN, VPN H, of the hotel; - for each call originated from a calling mobile station (1 a) of the hotel: - checking if the call is aimed to a called party belonging to the hotel VPN, VPN H " and in that case replacing the calling party number with the extension number (Ext A) assigned to the calling mobile station; - if the call is aimed to a called party not belonging to the hotel VPN, VPN H " replacing the calling party number with the external number (MainNum H) of the hotel PBX; - checking if the call is aimed to a called party belonging to the hotel VPN, VPN H " and in that case replacing the calling party number with the extension number (Ext A) assigned to the calling mobile station; - if the call is aimed to a called party not belonging to the hotel VPN, VPN H " replacing the calling party number with the external number (MainNum H) of the hotel PBX; - for each mobile terminated call aimed to a called mobile station of the hotel: - obtaining the extension number (Ext B) corresponding to the called mobile station of the hotel; - obtaining the MSISDN (MSISDN B) associated to said extension number (Ext B); - redirect the call through the mobile operator network to said MSISDN (MSISDN B) of the called mobile station. - obtaining the extension number (Ext B) corresponding to the called mobile station of the hotel; - obtaining the MSISDN (MSISDN B) associated to said extension number (Ext B); - redirect the call through the mobile operator network to said MSISDN (MSISDN B) of the called mobile station.