A data communication method between a POS terminal and a mobile communication device, such as a mobile phone, for providing a two-way data transfer within a cashless payment application, the method comprising the following steps: - tuning an NFC antenna of the POS terminal to a basic NFC frequency in the range from 13,00 - 14,00 MHz, - providing a removable memory card having its own contactless communication element, the method being characterized by the following steps: - the contactless communication element being tuned to a receiving frequency f1 and to a transmitting frequency f2, - inserting the removable memory card in a slot of the mobile communication device, the mobile communication device being energetically an operationally independent from the POS terminal, - providing a frequency converter within the transmission path between the POS terminal and the mobile communication device and in proximity of the NFC antenna, - in a case of data transmission from the POS terminal to the mobile communication device: - transmitting a data signal from the NFC antenna on the NFC basic frequency, - receiving the data signal by the frequency converter, - processing the data signal in the frequency converter, - transmitting the processed data signal from the frequency converter to the removable memory card in the the slot of the mobile communication device on the frequency f1, - in a case of reverse data transmission from the mobile communication device to the POS terminal: - transmitting a data signal from the removable memory card in the slot of the mobile communication device on the frequency f2, - receiving the data signal by the frequency converter, - processing the data signal in the frequency converter, - transmitting the processed data signal from the frequency converter to the NFC antenna on the NFC basic frequency, wherein - the frequencies f1 and f2 being different from the basic NFC frequency, - the frequency converter being powered during the data transmission with energy received from an electromagnetic field. - tuning an NFC antenna of the POS terminal to a basic NFC frequency in the range from 13,00 - 14,00 MHz, - providing a removable memory card having its own contactless communication element, - the contactless communication element being tuned to a receiving frequency f1 and to a transmitting frequency f2, - inserting the removable memory card in a slot of the mobile communication device, the mobile communication device being energetically an operationally independent from the POS terminal, - providing a frequency converter within the transmission path between the POS terminal and the mobile communication device and in proximity of the NFC antenna, - in a case of data transmission from the POS terminal to the mobile communication device: - transmitting a data signal from the NFC antenna on the NFC basic frequency, - receiving the data signal by the frequency converter, - processing the data signal in the frequency converter, - transmitting the processed data signal from the frequency converter to the removable memory card in the the slot of the mobile communication device on the frequency f1, - transmitting a data signal from the NFC antenna on the NFC basic frequency, - receiving the data signal by the frequency converter, - processing the data signal in the frequency converter, - transmitting the processed data signal from the frequency converter to the removable memory card in the the slot of the mobile communication device on the frequency f1, - in a case of reverse data transmission from the mobile communication device to the POS terminal: - transmitting a data signal from the removable memory card in the slot of the mobile communication device on the frequency f2, - receiving the data signal by the frequency converter, - processing the data signal in the frequency converter, - transmitting the processed data signal from the frequency converter to the NFC antenna on the NFC basic frequency, - transmitting a data signal from the removable memory card in the slot of the mobile communication device on the frequency f2, - receiving the data signal by the frequency converter, - processing the data signal in the frequency converter, - transmitting the processed data signal from the frequency converter to the NFC antenna on the NFC basic frequency, - the frequencies f1 and f2 being different from the basic NFC frequency, - the frequency converter being powered during the data transmission with energy received from an electromagnetic field.