Mayer Brown cured a nearly $1 billion headache for Latin America’s largest mobile phone carrier on Tuesday, persuading New York’s highest court to throw out $900 million in claims against America Movil brought by shareholders of the company’s Ecuadorean unit.

The plaintiffs — a pair of British Virgin Islands entities called Centro Empresarial Cempresa SA and Conecel Holding Ltd. — held a combined majority interest in Conecel, Ecuador’s mobile telephone company, in the late 1990s. The plaintiffs approached Mexican billionaire Carlos Slim, now America Movil’s chair, seeking outside capital for the company. Slim’s companies acquired a majority interest in the Ecuadorean company in 2000.