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What: Shares of Brightpoint (Nasdaq: CELL) have plunged today, down by 11% at their low, after the company announced that it lost a major customer.

So what: The company announced that one of its subsidiaries was notified that one of its big logistic services customers will begin transitioning to a different service provider in April continuing through the end of the year. The subsidiary had handled 6.8 million wireless devices for this customer in 2011, and 6.4 million devices in 2010.

Now what: Brightpoint expects the loss of this customer to decrease adjusted diluted earnings per share by $0.02 to $0.06 in 2012. On top of that, the company expects a larger-than-normal seasonal decline in units during the first quarter. Brightpoint is updating its full-year 2012 guidance as a result of these two developments, slashing its non-GAAP earnings-per-share forecast from a range of $1.07 to $1.17 to a lower $1.07 to $1.13.

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Fool contributor Evan Niu holds no position in any company mentioned. Click here to see his holdings and a short bio. Try any of our Foolish newsletter services free for 30 days. 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 has a disclosure policy.