AT&T Inc. is looking to sell its ownership of about 10,000 wireless towers in the United States and focus more on other parts of its telecom business, Bloomberg reported Tuesday. Under the plan, the company would lease back the tower space from the new owner, Bloomberg said. The towers could sell for about $5 billion, Bloomberg said, as the company heads into a major network upgrade costing $14 billion US. Possible buyers include Crown Castle International Corp., SBA Communications Corp. or American Tower Corp., the news agency reported. Owners of mobile towers can profit from the infrastructure by renting space to other providers. In Canada, Wind Mobile said this year that the incumbent wireless carriers' ownership of wireless towers has led to excessively high tower sharing rents for competing providers. The costs of putting up a new wireless tower are in the range of $350,000 to $1 million, depending on the type of tower and efforts to disguise it, people familiar with the issue said.