Enable the Consultative Transfer option in System Options >Agent Preferences > Call Handling.

Use Consultative Transfer when you want to announce the call before transferring the call to the third-party.
Note You cannot switch between two live calls during a consultive calls. To overcome this limitation, you can create a new work item in the Work List window using the Add Call button and switch between two active call. If you want to transfer the call to the caller in another work item, drag the call and drop it into the held call work item.

