Can You Hear Me Now?
This analysis from The Strategy Page mentions something which I always thought was critical, but no media outlet ever mentioned (at least that I saw.)
The Shia Arabs are less resolute, having been subject to particularly vicious repression between 1991 and 2003. But in majority Shia Arab areas, the Shia Arab police are able to deal with the anti-government forces. The police are aided by tribal militias (every household in Iraq is, by law, allowed one AK-47) and an alert population. The growing availability of cell phones has also made it harder for the terrorists to move freely among a hostile population. One phone call can bring dozens of men with assault rifles.
We really missed an opportunity early in the occupation, when we still had a good amount of goodwill, by not promptly getting the cell phone or land line telephone networks up. They're just starting to be effective now.
There were a lot of people who might have reported, in secret, guys running around in back alleys with RPG's, but they couldn't call anyone. As a result we forfeited a crucial communications link.