A mobile user apparatus and associated methods useful for conducting payment transactions wirelessly, such as at point-of-sale locations. In one embodiment, the mobile user apparatus is a cellular-enabled mobile device that includes a short-range passive radio frequency transceiver that when interrogated by a reader at the point-of-sale, issues a reply including information relating to an account of the user of the mobile apparatus that is to be debited for the payment. In one variant, the information stored on the mobile device is encrypted for security, and the mobile user apparatus is further configured to receive transaction data wirelessly in return.