Carlos Slims real estate firm, Inmobiliaria Carso, will buy ATT Incs equity stake in America Movil, tightening the Mexican tycoons control of his flagship telecommunications firm, according to a filing with Mexicos stock exchange on Friday. Slims Inmobiliaria Carso will buy more than 5.7 billion AA shares that have been held by ATT, equal to 8.27 percent of America Movils stock, the Mexican telecommunications firm said in the filing. The stake represents 23.81 percent of America Movils voting stock. Inmobiliaria Carso and one of its subsidiaries will also buy 72.8 million shares of commonly traded L shares, according to the filing.