THat should really have worked. as a last resort you could try the Telstra 2.2 update, since they use 850Mhz too.
Flashing with Optus now, then will try again. Also just noticed that the IMEI on the phone is different to the IMEI of the box it came in. I wonder if it got changed when flashing it at some point. This might be a stupid question but: Would the wrong IMEI on the phone stop it from connecting?
this is really a last gasp measure!
Also look at http://android.modaco.com/content-page/337130/zte-v9-light-2-2-update-now-available/page/200/
looks like your IMEI issue is mentioned and also someone has taken a ROM dump of the stock Telecom V9 ROM.
Ive never done a restore from a ROM dump, but that might be the way to go.