Final answer:
Webex Calling app is a soft client that supports calling from both desktop and mobile devices, and is part of the Cisco Webex suite which offers multiple communication tools.
Step-by-step explanation:
The correct description for Webex Calling app is C: a soft client for calling from desktop and mobile devices. Webex Calling is part of Cisco's Webex suite, which provides a range of communication tools, including calling, meetings, and messaging suitable for users on various devices. It is not only for Contact Centers or limited to desktop or mobile device conferencing exclusively.
The Webex Calling app integrates with the broader ecosystem of Cisco Webex services to enable comprehensive collaboration capabilities for its users.