Installing an adapter from AppExchange to work with third-party CTI systems, assigning the correct Salesforce users to the Call Center, and creating a softphone layout and assigning to user profiles are configurations that are needed for the softphone to work in Salesforce. A softphone is a customizable call-control tool that appears in the footer of the Service Console and allows agents to make and receive phone calls from within Salesforce. A softphone requires an adapter to connect with a third-party CTI (Computer Telephony Integration) system that handles the telephony functions, such as dialing, transferring, or conferencing. An adapter can be installed from AppExchange or developed using the Open CTI API. A Call Center is a record that defines the settings and behavior of the softphone, such as the adapter URL, the search preferences, or the call results. A Call Center must be created and assigned to the Salesforce users who need to use the softphone. A softphone layout is a layout that defines the fields and buttons that appear on the softphone for different call scenarios, such as inbound, outbound, or internal calls. A softphone layout must be created and assigned to the user profiles who need to use the softphone. Verified References: Service Cloud Consultant Certification Guide & Tips, Set Up Softphones in Salesforce Classic