Shared Call Appearance (SCA) is the sharing of a VoIP phone number across multiple devices in different locations.
SCA allows subscribers of VoIP services to have a single phone number for multiple devices in multiple locations associated with a given subscriber account. An account might be set up for different user devices and environments such as a smartphone with an app, a home phone and a PC at the work office.
Similar to analog phones provided for multiple lines and switching with private branch exchange (PBX) systems, VoIP phones and devices with VoIP software for SCA can support multiple lines. With SCA, any one of the devices configured for a number will ring for calls to the same number and any of the devices can place a call as well. While any device can make or receive calls, call control software only runs on one device at a time. Incoming calls are routed to the active device in the event of a second caller unless there are secondary numbers. Devices are configurable by software into groups to ring for any of the subscriber numbers.
Many ISP and VoIP providers currently offer SCA. With similar handsets, shared line appearance (SLA) is another type of VoIP technology. Both types of services often work on the same devices but may require different gateways.