Two North American mobile phone companies are trying to buy a controlling interest in Telecom Italia, Italy's largest telephone company, but there are complications. US company AT&T and Mexico's America Móvil have made a combined offer of €4.5 billion for a third of Olimpia, a holding company that owns 18% of Telecom Italia. Italian tire company Pirelli has been trying to sell their 80% stake in Olimpia because it has lost half its value since they acquired it in 2001. Italian politicians are opposed to foreign control of the phone company. After AT&T and America Móvil made their bid, Telecom Italia chairman Guido Rossi resigned his position; despite his reputation as a turnaround specialist, he could not come to an agreement with Pirelli chairman Marco Tronchetti Provera on the best financial strategy for the company.