From what I gather in the brief comment, the apartment complex only allowed AT&T to install cabling to the building, so those apartment buildings are only serviced by AT&T. The apartment complex will not allow another ISP to dig up their property to install internet service for tenants, leading to an exclusive AT&T monopoly. I've had friends in similar apartment buildings. Calling other ISPs operating across the street led nowhere, as those ISPs would just say "we do not service that address."