Method for using services of a mobile packet core network in a communication system comprising a mobile device, a core network, the mobile packet core network and a wireless radio access network (Wi-Fi), whereby the mobile device accesses the mobile packet core network via the wireless radio access network (Wi-Fi), wherein the mobile device, during setup of a connection of the mobile device to the wireless radio access network (Wi-Fi), determines whether the wireless radio access network (Wi-Fi) is a trustworthy wireless radio access network (Wi-Fi), and at least if the wireless radio access network (Wi-Fi) is not trustworthy, establishes a secure tunnel connection to a network entity of the mobile packet core network, wherein the network entity is a Virtual Private Network Server, a Tunnel Terminating Gateway or an evolved Packed Data Gateway (ePDG), for triggering a usage of a service of the mobile packet core network by an authentication entity of the mobile packet core network by using a certificate or credentials stored within the mobile device as credential towards the network entity, wherein the network entity of the mobile packet core network to which the mobile device establishes the secure tunnel connection uses the certificate or credentials stored within the mobile device to retrieve a MSISDN (MSISDN: Mobile Subscriber Integrated Services Digital Network) respectively a virtual MSISDN (vMSISDN) and/or an IMSI (IMSI: International Mobile Subscriber Identity) respectively a virtual IMSI (vIMSI) allocated to the user of the mobile device out of a database of the communication system, and passes the retrieved MSISDN respectively virtual MSISDN (vMSISDN) and/or IMSI respectively virtual IMSI (vIMSI) to the authentication entity of the mobile packet core network, which uses the MSISDN respectively virtual MSISDN (vMSISDN) and/or IMSI respectively virtual IMSI (vIMSI) for triggering a usage of a service of the mobile packet core network. wherein the mobile device, during setup of a connection of the mobile device to the wireless radio access network (Wi-Fi), determines whether the wireless radio access network (Wi-Fi) is a trustworthy wireless radio access network (Wi-Fi), and at least if the wireless radio access network (Wi-Fi) is not trustworthy, establishes a secure tunnel connection to a network entity of the mobile packet core network, wherein the network entity is a Virtual Private Network Server, a Tunnel Terminating Gateway or an evolved Packed Data Gateway (ePDG), for triggering a usage of a service of the mobile packet core network by an authentication entity of the mobile packet core network by using a certificate or credentials stored within the mobile device as credential towards the network entity, determines whether the wireless radio access network (Wi-Fi) is a trustworthy wireless radio access network (Wi-Fi), and at least if the wireless radio access network (Wi-Fi) is not trustworthy, establishes a secure tunnel connection to a network entity of the mobile packet core network, wherein the network entity is a Virtual Private Network Server, a Tunnel Terminating Gateway or an evolved Packed Data Gateway (ePDG), for triggering a usage of a service of the mobile packet core network by an authentication entity of the mobile packet core network by using a certificate or credentials stored within the mobile device as credential towards the network entity, wherein the network entity of the mobile packet core network to which the mobile device establishes the secure tunnel connection uses the certificate or credentials stored within the mobile device to retrieve a MSISDN (MSISDN: Mobile Subscriber Integrated Services Digital Network) respectively a virtual MSISDN (vMSISDN) and/or an IMSI (IMSI: International Mobile Subscriber Identity) respectively a virtual IMSI (vIMSI) allocated to the user of the mobile device out of a database of the communication system, and passes the retrieved MSISDN respectively virtual MSISDN (vMSISDN) and/or IMSI respectively virtual IMSI (vIMSI) to the authentication entity of the mobile packet core network, which uses the MSISDN respectively virtual MSISDN (vMSISDN) and/or IMSI respectively virtual IMSI (vIMSI) for triggering a usage of a service of the mobile packet core network.