Logging a call simply means actively recording the actions and states of a monitored call into a file on a disk. (An application that owns a call is also a monitor of that call.) Though limited call logging is performed by the call manager provided with Win32 Telephony, any application can be programmed to log a call that it is monitoring.
TAPI facilitates logging by allowing applications to monitor calls and by collecting information from other applications that are controlling calls. TAPI writes the information it collects into the LINECALLINFO structure, which can then be read by applications.