LEADING THE DAY: AT&T and T-Mobile now have a fight on their hands, after the Justice Department’s Wednesday announcement that it has filed to block the companies’ $39 billion merger, The Washington Post reported. AT&T immediately vowed it will challenge the suit, which says that joining the second- and fourth-largest wireless carriers in the country is bad for customers, jobs and innovation.

Now many are wondering what this means for the FCC review of the deal. In a statement, Federal Communications Chairman Julius Genachowski said that the DOJ’s action has raised serious concerns about competition, and an FCC official told The Post that the agency will “not undermine the DOJ’s process.”

This is the highest-profile Justice effort to be tough on antitrust, a campaign promise of the Obama administration. Since President Obama’s election, the DOJ has given its blessing to three major mergers — Comcast-NBC, Google-ITA and Ticketmaster-LiveNation — leading some to say its approach has been too timid, The Washington Post reported.

The challenge might be very bad news for T-Mobile and its parent company Deustche Telekom, Bloomberg reported, as the company’s low profits and shrinking customer base may not look as attractive now as it did when the company struck its deal with AT&T. Brian Barish, president of Cambiar Investors LLC, told Bloomberg that T-Mobile is now “damaged goods.”

And, as the AT&T bid for T-Mobile goes under inspection at a federal court, competitors and consumer groups are countering claims the merger will create jobs — a main tenet of the companies’ justification for the merger. On Thursday, Sprint released a study it commissioned by an economics professor at the University of California at Irvine, which found that jobs would certainly be eliminated as a result of the merger. The study also found that AT&T has a history of cutting jobs through its acquisitions.

Lawsuit accuses Microsoft of tracking:Lawyers in Seattle have filed a suit on behalf of a Windows Phone 7 user who alleges Microsoft tracks smartphone users against their will. The company has said in the past that it only collects geolocation data when a user explicitly approves it, but Reuters reported that this federal suit challenges those claims.

According to the report, the user says that Microsoft intentionally designed its camera software to record and transmit location data. In May, a mini-furor rose over claims that Apple’s iOS and Google’s Android systems kept tabs on users without express consent, something both companies denied.

Apple responds to pollution claims: Apple responded Thursday to claims that it is flouting its own standards on pollution, the Associated Press reported. A report Wednesday alleged that manufacturers who make the iPhone, iPad and other products use toxins and heavy metals that are harmful to public health and safety. In response, the company said that it committed to “driving the highest standards of social responsibility” among its supply chain partners and does its best to keep workers safe and use environmentally responsible practices.

Facebook leads Web engagement: New numbers from Nielsen show that Facebook is leading the pack on Web engagement, even though it had a smaller user audience than Google this July. The report, which uses a new metric to determine which Web sites draw the most unique visitors, found that users spent, on average, about five hours on the site last month. Overall, users spent an average of about 27 hours using the Internet, the report found.

Short product life cycles a consumer frustration: The average consumer takes about three to six months to research a gadget, often only to find that the device they’ve picked is about to see an upgrade, The Washington Post reported. With such short product life cycles, customers are often frozen with indecision over whether to buy now or wait for something better — something sociologists call “analysis paralysis.”