Abstract: A method for transmitting/receiving multimedia data between mobile devices comprising the steps: a) preparing a plurality of 4G and/or 5G mobile private networks each comprising a corresponding Home Subscriber Server (HSS) node for a 4G network or an Unified Data Management (UDM) for a 5G network, the mobile private networks of said plurality being mutually isolated to each other; b) preparing a plurality of mobile devices associated with users; c) registration of a group of mobile devices in the HSS or UDM node of a corresponding mobile private network to define groups of mobile devices whose connectivity is provided by separate and isolated mobile private network; d) preparing one or more central networks each comprising a corresponding HSS or UDM node and a corresponding Interrogating Call Section Control Function (I-CSCF) node; e) connecting one or more central network to two or more mobile private networks of said plurality.