Approaches for using and implementing transactions involving audio-equipped transaction cards reduce both data-management efforts and costs. In addition, certain applications further facilitate loyalty to the business entity that issues the audio-equipped transaction cards by, e.g., facilitating transactions with the card-issuing entity and/or selected business partners. One example embodiment is directed to audio-equipped personal cards and an approach to purchase agreement that involve activating an audio transmission from a transaction card to establish a point-of-sale purchase agreement. Data relating to the purchase agreement is communicated to an account/payment institution to confirm the purchase agreement, optionally in response to the customer's PIN being received. In another embodiment, a two apparatus (or “card”) approach involves retailers entering data via a retailer card that is useable by selected users (e.g., the retailer's representatives or employees). For such retailer and/or customer cards, various implementations are directed to different approaches for entering user information and/or security information such as customer PIN, a retailer-employee ID or PIN number.