All our phone calls will soon travel over the Internet. Here’s AT&T’s plan to test that out.

As the country upgrades its old, copper telephone lines to newer technology, the companies that operate those networks face a lot of unforeseen obstacles. The process is supposed to be complete by the later part of the decade and could enable new features in telephony such as high definition voice calls and improved 911 service. But it could also bring a range of consequences that nobody can really predict.

That's why telecom regulators have given carriers permission to start experimenting on a limited basis with a fiber-optic rollout. The transition to fiber-based networks -- which treat phone calls as packets traveling atop the Internet -- is being done in select markets of each phone company's choice. AT&T has now begun planning for its own trials. In a filing to the Federal Communications Commission, AT&T lays out its three-stage plan for how it will select its test sites. AT&T claims it won't simply test out the transition in places that are easy, but it remains to be seen which locations it has in mind.