WASHINGTON — Two phone companies – TerraCom Inc. and YourTel America Inc. – unwittingly posted the Social Security numbers, driver’s licenses and other sensitive data of up to 300,000 clients to the Internet, an investigation found, and federal regulators said on Friday they plan to fine the firms. As consumer data breaches go, the case – and its $10 million fine – is relatively small. But the incident is alarming because of how it unfolded: The companies participate in a government program called Lifeline, which subsidizes phone service for poor consumers.