TAPI 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 the number of rows and the number of columns. Both these numbers are zero if the phone device does not have a display. Use phoneSetDisplay to write information to the display of an open phone device, and phoneGetDisplay to retrieve the current contents of a phone's display.
When the display of a phone device is changed, a PHONE_STATE message is sent to the application function to notify the application about the state change. Parameters to this message provide an indication of the change.