> There are still problems - e.g. BT is often accused of milking OpenReach rather than investing in the network.
The caveat is perhaps the opposite of what you suggest. Unbundling works okay in the U.K. because BT OpenReach has been allowed to be quite profitable. (Their profits as a percentage of revenue are between TWC and Comcast.) Unbundling in the U.S. failed, in contrast, because the FCC set wholesale rates so low there was basically no incentive to invest in DSL networks.
It's my theory that stuff that works in other countries fails in the U.S. because everyone is so ideological. In the U.K., the privatization of BT was preceded by tons of economic studies analyzing how to balance broadband availability and price against the need to make investing in broadband a profitable endeavor. In the U.S. it's entirely ideological. Pro-business free marketers on one side versus people who see broadband as a social justice issue, economics be damned. We lurch form one mode to the other based on who happens to be in power.