Not that I'd ever advocate circumventing a mobile carrier because, unlike virtually every other mobile carrier on the planet, it won't release operating system updates for Windows Phone 7 (yes, AT&T, you are that carrier), but there is now a handy tool that let's you do just that.
Windows Phone Secrets has a story on this simple do-it-yourself utility. Chris Walsh wrote the program that allows the update in spite of a recalcitrant carrer and provide the utility at his blog. Simple Mobile Review provides a documented, step-by-step guide to using the utility.
Conspiracy theories already exist, but the utility Chris wrote was only possible after Microsoft released a support tool for Windows Phone 7. Maybe it was coincidental that the tool allowed easy bypass of a non-cooperative carrier. Or maybe Microsoft put a tool out there knowing precisely what could be done with it. Seems a bit much to say that it was lucky coincidence that a tool capable of circumventing carrier update blocks was so easy to use for that purpose that it took all of one day to write the program to implement it for that purpose. But I'm no programmer, so how would I know?
I consider this (and by "this," I mean jabbing a stick in AT&T's eye) to be part of my role as a pro-consumer advocate. But these tips are about self-empowerment.
I have it on exceeeeedingly good authority that this update method works flawlessly. Yay! The chevronWP7.Updater is currently offline. Awwww. It may just be that the developer is revising the utility. Or maybe some thugs in ties and suits (wait, that's me...rats), errr, some esteemed legal counsel for some offended entity issued the good ol' cease and desist (redundant) demand. Anyhow, it works, and it's out there. So long as the Microsoft utility can pull updates directly, this may prove to be the ultimate carrier workaround.
If you can't find it at the original source, search for ChevronWP7.Updater at places like XDAdevelopers. It's only a matter of time before a mirror springs up.