Abstract: A method for exchanging data concerning an electronic transaction between two entities, includes: a step which consists in determining and booking an origin address (TPOA) in conformity with a bidirectional mobile telephony (GSM) digital messaging service protocol (SMS); a step which consists in sending in accordance with the protocol (SMS), an offer message (OFFER_SMS) of the transaction (TR), the offer message (OFFER_SMS) being sent from the first entity (MW) and addressed to the second entity (CL); and a step which consists in sending, from the second entity (CL) and addressed to the first entity (MW), a reply message comprising an information (REP) representing acceptance or rejection of the transaction.