The Call Stacker is a small unit that records calls that cannot be sent to all required zones because some are occupied by a higher priority call. The unit can store up to 16 calls in high-quality format with a maximum of three minutes for each call, including chimes and pre-recorded messages. Playback of a call can start while it is still being recorded. The unit can record and/or playback up to eight calls simultaneously. More units can be added to a system in order to increase the number of recordable calls. Units can be connected to the Praesideo network at any place