HWND pascal GetDlgItem(HDLG hDlg, WORD id)

  This function returns the handle associated with a dialog box control.

Parameters
  hDlg is the handle of the dialog box which contains the specified control.
  id is the identifier of the control that we want to query. (The id
   is not the same thing as the handle.)

Returns
  The handle associated with the control, or NULLHWND if the id
parameter did not specify a valid control.

Example

HWND hEdit;
   case WM_INITDIALOG :
     hEdit = GetDlgItem(hDlg, ID_PHONE);
     SendMessage(hEdit, WM_SETTEXT, 0, (LPSTR) "(123) 456-7890");