Iliad, a telecom business based in France, has made an unsolicited offer to purchase T-Mobile U.S. The company submitted the offer to T-Mobile's board within the last week. It is offering $15 billion in cash for a controlling 56.6% stake in the company. Iliad's role in the French mobile market is similar to T-Mobile's in the U.S. market. It sees T-Mobile as a natural fit and a way to break into the U.S. market. "The U.S. mobile market is vast and attractive," said Iliad in a statement. "T-Mobile has successfully established itself in the market by positioning itself, in many respects, in a similar way to Iliad in France." Iliad's offer complicates Sprint's interest in T-Mobile. Sprint and T-Mobile are believed to have agreed to the broad strokes of an acquisition, but are still hammering out details. Sprint has not made a formal offer for T-Mobile, but may have to accelerate its plans with Iliad's offer now on the table. T-Mobile has not commented publicly on Iliad's offer, but it did report second quarter earnings today. T-Mobile added 1.5 million new customers this quarter and has expanded the availability of VoLTE nationwide as of today.