NEW YORK (The Deal) -- Carlos Slim holding company Inmobiliaria Carso is buying an 8.3% stake in the Mexican tycoon's America Movil (AMX - Get Report) phone company from AT&T (T - Get Report), ending a 20-year relationship as priorities shift among the world's telecommunications giants.

The holding company is paying $5.57 billion for the stake, including $4.57 billion upfront and the remaining $1 billion within 60 days of the closing. The minority holding carries 24% of America Movil's voting rights and contains a mixture of voting and non-voting shares. Slim already owns a majority of stock in America Movil, where he is chairman.

AT&T must sell the stake as it fights to complete its $67.1 billion acquisition of pay-TV provider DirecTV Group Inc. The acquisition, if it wins regulatory approval, would give AT&T a significant stake in Mexico's biggest satellite broadcaster and make it a direct competitor to America Movil in Mexico as well as South America, creating a conflict of interest.

"America Movil recognizes the great value that the partnership with AT&T had for both companies for more than 20 years," the Mexican telecom said.

AT&T has said it wants to use $7 billion from asset sales to fund its DirecTV acquisition.

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Phone companies are becoming increasingly international and are also branching out into content delivery as part of their now-legacy business of providing broadband Internet access. Slim himself has expanded into Europe by buying a minority stake in the Netherland's Royal KPN NV as well as working to gain control of Telekom Austria AG.

AT&T has stuck primarily to the U.S,. but will gain DirecTV's 41% investment in SKY Mexico, that country's biggest satellite broadcaster.

However, U.S. politicians are wary of the AT&T/DirecTV deal because they fear it would stifle competition as the two currently compete to provide broadband and entertainment content to customers.

AT&T has previously run afoul of regulators -- bureaucrats also scuppered its proposed 2011 acquisition to T-Mobile USA Inc., the U.S. mobile phone division of Germany's Deutsche Telekom AG.