At this very moment no one knows exactly if the story is true or not.
The initial article most bloggers referred to (News24.com) is down, even the the title of the page which said (with a blank page after some hours) "Rumsfeld bans phone cameras" is blank now and says only: "http://www.news24.com/News24/World/Iraq/0,,2-10-1460_1531277,00.html".
Additionally the major concern is:
I'd also like to see independent confirmation from a non-AFP newswire source, but I find it very hard to believe that an order affecting 150,000 soldiers at an individual level (i.e. each one has to be told to put away their camera) is somehow "discovered" by a UK "Business" newspaper and not discussed in any American mainstream paper or national security trade publication. (Andrew Leyden from Penguinsix.com, Link)
See also "I now vote Camera ban as a joke" and "You have to wonder sometimes..."
So as long as there is no other confirmation: the story is probably a fake. Just like this story: THE DAILY FARCE, "New Abuse Pictures Emerge; Rumself Prohibits Digital Cameras In Iraq".
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[Update 10 min. after posting: according to BoingBoing it´s a fake]
This morning, I asked a Defense Department spokesperson whether or not the reports of a phonecam ban were true. This spokesperson said that these reports were technically inaccurate -- that the Pentagon is not issuing a new ban on camera phones per se, but that a Directive 8100.2 was issued on April 14 establishing new restrictions on wireless telecommunications equipment in general.