TAPI is a Windows API which provides access to incoming and outgoing calls. In addition, calls can be made and controlled. To use TAPI, the manufacturer of the telephones/switchboards must provide a TAPI driver. PC CADDIE then communicates with the TAPI driver via the Windows TAPI interface. Not every TAPI driver has the same version and the same functionality, therefore additional configurations may be needed. Each TAPI configuration has its own particularities.

The TAPI implementation in PC CADDIE can monitor and make calls. Incoming and outgoing calls are collected and stored in the PCC_CALL.DBF database. PC CADDIE can display a pop-up with this information at the user's request, including information about the caller. Thus, the user knows who is calling, and can automate the creation of a CRM entry for the call. In addition, the user can make calls to persons already stored in the database by clicking on the telephone icon. This is also recorded in the database.

TAPI drivers from version 2.0 are currently supported, disregarding of the manufacturer. However, not all drivers provide all the necessary information; a definitive compatibility can only be determined after a test.