The steps were:
- Buy a Sierra MC8775 WWAN card on eBay $AUD110 and while waiting for delivery:
Download and install HP WWAN drivers (the MC8775 is sold as a HP card) - free
Download Sierra's generic 3G watcher sofware and install it - free
Ask Zender for his magic BIOS upgrade for my X300 and download it as an iso image file - free
Burn the iso onto a CD, use the Lenovo support site to roll back my 1.08 BIOS to 1.06
Use Zender's CD to flash the BIOS back to 1.08
Visit Telstra and get a SIM for a casual plan with 150MB data pack ($AUD30/month can be cancelled at any time)
Download the X300 hardware maintenance manual and study how to remove and replace a WWAN card (pointy nose tweezers are a definite advantage)
Install the card and the SIM
Boot up the X300 and watch the HP drivers load (there are a lot of them - card, ports, modem)
Watch the Sierra watcher program find the Telstra 3G network and click connect - voila!
Success at last



