Technology is disclosed for associating content objects (e.g., paper documents, audio and video files, etc.) with corresponding information and/or action. One arrangement employs an architecture comprising a registration server, a router, and one or more product handlers. Identifiers for the content objects can be obtained in various ways, including decoding a digital watermark, deriving an identifier by hashing music data, sensing machine-readable data such as RFID or barcode data, etc. One particular method involves applying an algorithmic process to produce music- or video-content-identifying data; wirelessly sending the content-identifying data from the device in one or more packets including XML compliant data; and, as a consequence, receiving data back. By reference to this data, the receiving device presents information to a user that identifies a title of the content, and a performer of the content. Also presented are one or more features selectable by the user to obtain further information relating to the content, or different content. The technology is suitable for use with handheld devices, including cell phones and media players.