TSPI provides access to a phone's display. The display is modeled as an alphanumeric area with rows and columns. A phone's device capabilities indicate the size of a phone's display as number of rows and number of columns. Both these numbers are zero if the phone device does not have a display. The TSPI_phoneSetDisplay function writes information to the display of an open phone device. TSPI_phoneGetDisplay returns the current contents of a phone's display.
When the display of a phone device is changed, the service provider sends a PHONE_STATUS message to the tapi32.dll callback function to notify it about the state change. Parameters to this message provide an indication of the change.