A method and system are disclosed for booking and paying a retailer having a POS, which can be a low cost thin client computer system, connected to a transaction server storing confidential user information including a retailer identification, a user code and a user wireless device phone number, said method comprising the steps of receiving at the transaction server, from the user wireless device which can be a common cellphone, an SMS containing a retailer identification, reading at the transaction server the phone number of the wireless device communicated by the carrier transporting the SMS, authentifying said phone number and retailer identification with the stored confidential user information and sending the user confidential information to the retailer POS, the user entering on the POS the user code and the POS reading and authentifying the user code with the user confidential information received from the transaction server, the retailer entering the payment information on the POS and sending it with user information to the transaction server.