Congressional lawmakers can look at Massachusetts and Tennessee for guidance as they craft a national plan to restrain costs and cover the nation's estimated 50 million uninsured. In Massachusetts, nearly every resident has health insurance, but doctors are turning away new patients, costs to the state are climbing, and thousands have paid tax penalties for being uninsured. In Tennessee, that state's much smaller program hasn't cramped the budget, but few people are buying the new insurance even though premiums are as cheap as a monthly cell phone bill.