Method for exchange of secure messages between at least two terminals (USER A, USER B) capable of communicating with a 2G/3G cellular telecommunications network belonging to at least two operators (Oper A, Oper B), said terminals (USER A, USER B) each comprising a trade module (MM user USER A, MM user USER B) capable of managing and generating public and private keys, said 2G/3G cellular telecommunications network comprising two messaging modules (M Mess A, M Mess B) each belonging to an operator (Oper A, Oper B), two trade modules (MME A, MME B) capable of managing and generating public and private keys, the method being characterised in that it comprises: a) a step for generation of public and private encryption keys (CPu UA, CPR UA) from PDP contextual data extracted by the trade module (MM USER A) of the network to which the first user of the terminal (USER A) is connected, b) a step for generation of the same public and private encryption keys (CPu UA, CPR UA) from the PDP contextual data extracted by the trade module (MM user A) of the operator (OPER A) and for transmission of the public key (CPu UA) to the messaging module (M Mess B) of the operator B, c) a step for generation of public and private encryption keys (CPu UB, CPR UB) from the PDP contextual data extracted by the trade module (MM user USER B) of the network to which the second user of the terminal (USER B) is connected, d) a step for generation of the same public and private encryption keys (CPu UB, CPR UB) from the PDP contextual data extracted by the trade module (MME B) of the operator (OPER B) and for transmission of the public key (CPu UB) to the messaging module (M Mess A) of the operator A, e) a step for encryption of the message by the terminal (USER A) with the public encryption key generated in step a), f) a step for decryption of the message by the messaging module (M Mess A) of the operator (Oper A) with the private encryption key of the trade module (MME A) generated in step b), g) a step for encryption of the message by the messaging module (M Mess A) of the operator (Oper A) with the public encryption key of the trade module (MM B), h) a step for decryption of the message by the terminal (USER B) with its private encryption key. a) a step for generation of public and private encryption keys (CPu UA, CPR UA) from PDP contextual data extracted by the trade module (MM USER A) of the network to which the first user of the terminal (USER A) is connected, b) a step for generation of the same public and private encryption keys (CPu UA, CPR UA) from the PDP contextual data extracted by the trade module (MM user A) of the operator (OPER A) and for transmission of the public key (CPu UA) to the messaging module (M Mess B) of the operator B, c) a step for generation of public and private encryption keys (CPu UB, CPR UB) from the PDP contextual data extracted by the trade module (MM user USER B) of the network to which the second user of the terminal (USER B) is connected, d) a step for generation of the same public and private encryption keys (CPu UB, CPR UB) from the PDP contextual data extracted by the trade module (MME B) of the operator (OPER B) and for transmission of the public key (CPu UB) to the messaging module (M Mess A) of the operator A, e) a step for encryption of the message by the terminal (USER A) with the public encryption key generated in step a), f) a step for decryption of the message by the messaging module (M Mess A) of the operator (Oper A) with the private encryption key of the trade module (MME A) generated in step b), g) a step for encryption of the message by the messaging module (M Mess A) of the operator (Oper A) with the public encryption key of the trade module (MM B), h) a step for decryption of the message by the terminal (USER B) with its private encryption key.