Abstract: The invention relates to a system which can be used for exchanging short multimedia messages between two or more users. The system is used, without distinction, for client-server implementations (31, 32, 33) or for server-free client-client implementations (41, 42). The system has the following essential technical features: (i) the session is established (311, 411) when a first client presses a user button and is ended (313, 413) when said first user releases said button; (ii) at the start of the session (311, 411) a list of all the participants is transmitted; (iii) at the start of the session (311, 411) a global session identifier is transmitted; (iv) the clients receiving a PTT message sent by the aforementioned first client optionally reply after receiving said list and identifier.

Abstract: Disclosed is a method for the secure access of a mobile device to a nearby client device that includes the following: 1. the mobile device generating, at the time of receiving a determined stimulus, a code comprising security credentials and a contact address in a server; 2. representing the code and address in the screen of the mobile device; 3. the client device detecting and extracting the represented information; 4. the client device connecting to the contact address using the credentials; 5. the client obtaining the information contained in the contact address. By applying the method the server device can indicate the mode of access to the contents or services associated with the device, both if they are offered directly from the device itself and if they are offered from another external element.