I can confirm this guide works flawlessly on at&t Quantum!! It is very simple and takes about 30 minutes to complete. If you want tethering on your non-Telstra Quantum, there is no reason not to just this and you won't regret it!
---------- Post added at 04:39 PM ---------- Previous post was at 03:49 PM ----------
Actually I have to somewhat qualify my previous statement. The installation went perfectly, however there are some after effects. For instance, my data connection no longer works and as stated previously by others, MMS no longer works. Also, I noticed, as I suspected, the marketplace is region specific and some apps are not available with the Telstra ROM. An example would be the Xbox Extras apps. The marketplace thinks I am outside the US even though I am definitely in the US on at&t network. DAMN! This is alittle annoying and it makes me wonder what other apps I am not able to get access to with this ROM. OH well, I guess there are positives and negatives, but wifi tether is worth it in my opinion.
Just be aware, there are some minor consequences. I'm sure I can get most everything working again, but may take some tinkering.