AT&T promised (to get a merger approved) to offer DSL service to everyone in its service areas, but refuses to install new equipment to do so.

You can't expect a big company to keep its promises unless it is punished directly when it doesn't. If AT&T were find $100,000 per person per year, for each person entitled to DSL and waiting for it, and the victim got half of that as compensation, AT&T would fix this.