Britain's Prime Minister David Cameron has proposed some of the most sweeping changes to the country's National Health Service in its history. The government says the changes are designed to give doctors more say in running the NHS, and patients more freedom of choice. But critics point out that NHS doctors will be allowed to take more private patients, and some hospitals will be allowed to opt out of the NHS entirely -- raising the possibility that U.S. HMOs might come in to fill the vacuum.