The call icon that is present corresponding to a contact is to initiate Click2Call.

What is a Click2Call?
An instant calling widget, strategically placed in your app to help you get in touch with leads while they’re looking you up. With Click-to-Call, you can connect with leads, right away, to increase your conversion time. As soon as a visitor submits his number, we bridge a call between your agent and the visitor (numbers registered in NDNC are not dialed). These calls are free of cost to your potential customers.

A call is directly placed to the agent. On successfully picking the call, the call is placed to the customer.