Of course, those can be blocked too, and often are.  Twitter’s ancillary sites are working — to the extent they still are — only because the censors have their hands full at the moment.  But the PC changes the equation on both sides: within and outside of Iran.

Inside Iran, people can load new software on their PCs to try to get around blocks.  Find a copy of something like the xB browser online, or modify your current browser to work with software like Tor, and you can try directing all your Web access through intermediaries that aren’t blocked.  If you find one that works, all your surfing can end up unblocked.  If people were using today’s mobile phones for Internet access instead of PCs, this wouldn’t be possible, because most mobile phones, even if they can hook up to a wireless Internet access point, won’t run outside code, or only run outside code approved by the vendor.  (The jury’s still out on how easily one can install outside code on a phone running Google’s Android OS.)

Even more important than the options available to someone inside Iran are the options for those everywhere else.  Many people have been eager to show support for those in Iran who want to evade the government clampdown on news, both in and out.  Thanks to the PC they can do more than color their personal avatars green.  If you have a PC and want to help, you can find instructions on how to download software that will turn your PC into a way station between Iranian citizens and the rest of the Net.  Two minutes ago you were playing Quake, and now you’re donating bandwidth and computing cycles to the free movement of bits — and you can even go back to playing Quake again.  And discussions are under way to reconfigure the just-released free Opera browser so it can serve as a proxy. [Update: Al Billings at Mozilla is thinking through the same questions for Firefox.]

That’s extraordinary.  The computing machines we buy are descendants of the old hobbyist machines of the 1980’s, which assumed people would get them so they could tinker with them, and those vestiges turn out to be crucial at a time like this.  We’re lucky to still have so many home PCs out there.  Our work ones are often locked down — your neighborhood IT department would have a heart attack if it found you running a proxy server, since it would worry about the security of the corporate intranet.  Most schools don’t allow their students to run new code in a computer cluster, and libraries are locked down, too.  (Indeed, all three of these places typically have their own content filters installed!)  Thanks to the PC, people can help forge new civic technologies — ones that succeed to the extent that people are willing to participate in them.

Perhaps soon we’ll see even more profound ways to transform access to the information grid.  Researchers have been puzzling through “wireless ad hoc mesh networking,” which allows devices to connect to each other without needing an Internet Service Provider to run interference.  If anyone is connected to the larger Internet, everyone else nearby — and everyone near everyone else nearby, etc. — can connect.  This is the method used by the One Laptop Per Child project to allow the PCs they are sending to kids in developing countries to share data with one another even if there’s no Internet drop point available.  Imagine that technology redeployed to this situation — and it can be, if someone writes or adapts the right software.  Our PCs have radios in them that can talk to one another, not just to an “official” access point; you may even recall seeing others’ computers in your wi-fi access list when trying to find a way to get online while on the road.  A little tweak here and there and it can start working — for school kids in Brazil, for hurricane refugees running laptops on battery power, and for citizens in Iran facing otherwise-limited Net access.

A green avatar is just the beginning — so long as we maintain our somewhat accidental ubiquitous infrastructure of generative, reprogrammable boxes, a legion of hackers ready to reprogram them to social ends, and a citizenry ready to donate some bandwidth and cycles to a good cause.