Without a BlackBerry plan your device with be very restricted and most Blackberry applications will not work. Also please be aware that if you download anything without a data or Blackberry plan you will be charged very high fees. It is possible to manually set an APN on a BlackBerry device but this doesn't always work correctly. If possible can you locate someone who has a BlackBerry plan on Optus? If you can insert their SIM for a few minutes and it will download the service books to configure your device (include Optus Zoo Browser).