Search "net2phone for Salesforce" in AppExchange . (Make sure you are logged in to App Exchange)
Click the net2phone icon.
Click Get it Now.
Click Install in Production.
Read and accept the Terms of Condition.
Click Confirm and Install.
Sign in the Salesforce (via redirect).
Choose Install for All Users.
Click Install.
Once the installation is complete, click Done.
Click the gear icon in the top right corner, then click Setup.
Type “Call” in the Quick Find search tool.
Click the Softphone Layouts tab on the left side.
Click the New button.
Name the layout and click the Default Layout checkbox.
Click Save.
Type "Call Centers" in the Quick Find search tool.
Click the Call Centers tab.
Click CTI Adapter.
Click Manage Call Center Users.
Click Add More Users.
Click Find to bring up all available users.
Select users by clicking the checkbox next to their names and clicking Add to Call Center.
Navigate to the app that needs to be edited and click the down arrow on the right side, then Edit (*Note, the app type must be “Lightning”).
Click Utility Items tab at the top left.
Click Add Utility Item.
Select Open CTI Softphone from the list.
Click Save.
If the net2phone app appears blank when opened from the Utility Bar you will need to disable clickjack protection for customer Visualforce pages with headers disabled.
If users can’t be added to the CTI Adapter Call Center because they used the net2phone app in Salesforce classic, check the following: