The largest mobile operator in the U.K., EE , announced on Monday that its CEO Tom Alexander has resigned "for personal reasons and to pursue other interests," after just one year in the top job.

Alexander's replacement will be Olaf Swantee, who is currently executive VP of European activities and sourcing at Orange (NYSE: FTE) and a board member of Everything Everywhere. Swantee will take up the CEO role on September 1.

Everything Everywhere, which is the U.K. joint venture of Orange UK and T-Mobile (UK) , had 27.7 million subscribers at the end of March this year. The company officially launched on July 1, 2010 and is in the process of combining certain network assets to remove duplication and reduce costs.

According to Everything Everywhere's first-quarter results for 2011, revenue and customers are both on the decline: Revenues fell by 2.7 percent compared with the first quarter in 2010 and the customer base dipped by 0.6 percent compared with the year-ago quarter.

Why this matters
Alexander's resignation is a surprise. The timing of the announcement -- which comes just before France Telecom's second-quarter results release on July 28 -- invites speculation about the joint venture's financial health and strategy execution.

Also, the performance of Everything Everywhere in the U.K. has bigger implications for its parents Deutsche Telekom AG (NYSE: DT) and France Telecom, which have plans for more cooperation across their European operations through a new procurement joint venture. (See DT & FT Deepen Ties.)

For more
Here's the latest news about the U.K.'s mobile giant:

• Everything Everywhere Outsources to T-Systems
• Everything Everywhere, BT Test LTE
• Everything Everywhere Picks Huawei
• Everything Everywhere Reports 9M
• UK Giant Eyes LTE in Vendor Review
• UK Mobile Giant Flexes Its Muscle
• Eurosqueeze?
• Orange, T-Mobile Do Everything Everywhere

— Michelle Donegan, European Editor, Light Reading Mobile