Could Iran Shut Down Twitter?

Publius thinks so:

 [Tweets are] essentially being sent to "middlemen" proxy servers -- which, in turn, allows the information to pass "in disguise" through the filter.  It's like a digital Underground Railroad...But here's the thing -- they're only getting through because Iran has (for now) left its networks open, even though the government has apparently tried to limit bandwidth to prevent videos and pictures from getting out.