PABX3 will only show calls in VT100 if you are using the serial connection option:
OPTIONS -> COMMUNICATIONS, select the required comport number
Ensure 'Offline' is not ticked.
If the TCP and COM display (to right-hand corner) is RED, please go to
OPTIONS -> Network, in the 'Remote PABX' section ensure that no options is ticket.
If any, untick and click on 'SAVE'.
Now the COM display should be green and you should have call details displaying under 'Call Data'.
If not, check the VTI100 screen and ensure that your setting is correct (for example baud rate and plugin).
Also see:
http://forums.datatex.co.za/viewtopic.php?f=28&t=2282&p=2288&