Microsoft Corp. struck a $7 billion deal to acquire Nokia Corp.'s core cellphone business, a bold move to try to catch up in a fast-growing mobile business that is now dominated by Samsung and Apple.

The deal comes on the heels of announcing the planned retirement of Microsoft Chief Executive Steve Ballmer. As part of the deal for the devices-and-services business, Microsoft will bring aboard several executives who could be contenders for Mr. Ballmer's job.

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