An apparatus having a voice-estimation (VE) interface that probes the vocal tract of a user with sub-threshold acoustic waves to estimate the user's voice while the user speaks silently or audibly in a noisy or socially sensitive environment. In one embodiment, the VE interface is integrated into a cell phone that directs an estimated-voice signal over a network to a remote party to enable (i) the user to have a conversation with the remote party without disturbing other people, e.g., at a meeting, conference, movie, or performance, and (ii) the remote party to more-clearly hear the user whose voice would otherwise be overwhelmed by a relatively loud ambient noise due to the user being, e.g., in a nightclub, disco, or flying aircraft.