Elk has released a new flush-mount speaker/microphone combo unit which fits in a single gang junction box.  From their announcement:

ELK-M1TWSF flush mount Speaker/Microphone combo is designed for two way listen-in systems.  The compact, single gang design allows the unit to go virtually unnoticed.  Works well with Elk Products Two Way Listen-In amplified interface, Elk-M1TWA, and non-amplified Interfaces, Elk-M1TWI and Elk-M1EZ8TWI, as well as interfaces by other manufacturers.

At the time of this writing, pricing information was not available.  Features and specifications follow below.

Features

• Compact, single gang design allows unit to go virtually unnoticed
• Simple four wire connection
• High Sensitivity
• Up to 12 may be connected to one M1 Two Way Listen-In Interface

Specifications

• Operating Voltage: Powered from M1TWA, M1TWI, or M1EZ8TWI
• Current Draw. 5mA each
• Speaker Impedance:  32 ohms
• Speaker Rating:  12 Watts Nominal
• Size: 4.81" x 3.13" x 1.75"
• Color:  White