They did it on purpose.
As has been noted, no matter how much wireless communications we have, at some point, we are all connected to a big wire somewhere.
Reports about the incident speculate about how vulnerable the communication and electrical systems are in the U.S., and AT&T is offering a hundred thousand dollar reward for information leading to the arrest of those responsible.
Hundred grand. You think they are concerned?
On some level, I find this very interesting, another case of life imitating art. Seven years before 9/11, Tom Clancy's novel, Debt of Honor, has a Japanese terrorist crashing a jet into the U.S. Capitol, killing most of Congress and the administration, and making Jack Ryan the President.
Eight years ago, in Net Force: Cybernation -- a book in which I had some part -- there is a cyber-terrorist organization that attacks fiber-optic lines. (I even had a scene in a book that never was published in which a man crashes a plane into the Statue of Liberty, also years before the Twin Towers.)
I don't think this makes me or Mr. Clancy Nostradamus by any means; but when Condi Rice told the world that nobody could have ever predicted that terrorists would hijack planes and fly them into buildings, she was, like much of what she had to say during her term under George Bush, wrong. People had already done so.
Not just a failure of the imagination, but plain old ignorance.