Did Stephen Elop know what he was signing up for when he left Microsoft (Nasdaq: MSFT) to take over as CEO of Nokia (NYSE: NOK) in September? I'm not so sure.

Four months into his reign, Elop and his team this week canceled plans to bring the X7 smartphone to AT&T's (NYSE: T) network here in the U.S., The Wall Street Journal reports. No official word has been given, but no one's denying it, either.

Perhaps that's because the story is believable. Seriously, is there anyone left who's surprised by Nokia's failures to penetrate the U.S. market? American users have been turning to domestically designed options for months now. Google's (Nasdaq: GOOG) Android OS has been the primary benefactor, while Research In Motion's (Nasdaq: RIMM) BlackBerry OS has fallen from leader to laggard. According to the Nielsen company, its share of U.S. customers purchasing a phone in the last six months has declined from 35% in June to 19.2% in November.

So Nokia isn't alone in its failure. And yet there's an increasing body of evidence that, like ancient Rome, the Finnish phenom's once-vaunted global empire is crumbling.

Over at Computerworld, reporter Richi Jennings cites data from a mobile analytics company comprised of ex-Nokia executives who found that only 6% of current U.S. Symbian (i.e., Nokia) users surveyed would purchase another Symbian device. Most were planning to switch to the iPhone. Android and Windows Phone 7 were also named as alternatives.

Excuse me? Just 6%? If that's even within spitting distance of accurate, everything that drives earnings at Nokia from here on is under threat. At the very least, carrier agreements could become less generous and drive down hardware margins. Less cash would flow through the business as a result, hurting investors' chances to realize market-beating returns.

Now it's your turn to weigh in. What do you think of Nokia canceling the X7 here in the U.S.? Is the business facing a global threat? Please vote in the poll below and then leave a comment to explain your thinking.

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Fool contributor Tim Beyers is a member of the Rule Breakers stock-picking team. He owned shares of Google at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. You can also get his insights delivered directly to your RSS reader. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool owns shares of Google and Microsoft. The Fool is also on Twitter as @TheMotleyFool. Its disclosure policy doesn't want to see any paperwork on this, OK?