A method for roaming between cellular carriers, the method comprising: obtaining from a Home Public Land Mobile Network, home network, at least one International Mobile Subscriber Identity, IMSI number; characterized in that the method further comprises the following steps: generating an identification code and sending it to the home network with an indication of a location of the identification code (i) in a Packet Data Protocol, PDP of a context request response, or (ii) in a registration request when authenticating a User Equipment, UE's SIM, Subscriber Identification Module, card or IMSI number; configuring a UE with instructions to insert the identification code into a specific mandatory characteristic of the PDP context request response or registration request, in a response to a context request received from the home network; requesting the home network to mark a UE's identification element, in relevant serving data nodes, presenting the identification code located in the specific mandatory characteristic of the PDP of a context request response or registration request, to distinguish it from other UEs; and requesting the home network to: (i) direct incoming roaming data from the UE using a marked UE identification element to a mediating roaming service server when the indication of a location of the identification code is in the PDP context request response, or (ii) change data handling and routing by reflecting user SIM card profile data or user SIM card profile identification which is stored in relevant serving data nodes, in the data gateway nodes, when the indication of a location of the identification code is in a registration request, wherein the changing is performed based on the identification code. obtaining from a Home Public Land Mobile Network, home network, at least one International Mobile Subscriber Identity, IMSI number; characterized in that the method further comprises the following steps: generating an identification code and sending it to the home network with an indication of a location of the identification code (i) in a Packet Data Protocol, PDP of a context request response, or (ii) in a registration request when authenticating a User Equipment, UE's SIM, Subscriber Identification Module, card or IMSI number; configuring a UE with instructions to insert the identification code into a specific mandatory characteristic of the PDP context request response or registration request, in a response to a context request received from the home network; requesting the home network to mark a UE's identification element, in relevant serving data nodes, presenting the identification code located in the specific mandatory characteristic of the PDP of a context request response or registration request, to distinguish it from other UEs; and requesting the home network to: (i) direct incoming roaming data from the UE using a marked UE identification element to a mediating roaming service server when the indication of a location of the identification code is in the PDP context request response, or (ii) change data handling and routing by reflecting user SIM card profile data or user SIM card profile identification which is stored in relevant serving data nodes, in the data gateway nodes, when the indication of a location of the identification code is in a registration request, (i) direct incoming roaming data from the UE using a marked UE identification element to a mediating roaming service server when the indication of a location of the identification code is in the PDP context request response, or (ii) change data handling and routing by reflecting user SIM card profile data or user SIM card profile identification which is stored in relevant serving data nodes, in the data gateway nodes, when the indication of a location of the identification code is in a registration request, wherein the changing is performed based on the identification code.