On Thursday, the Federal Communications Commission is expected to take its first major step toward letting AT&T and other carriers replace the country's traditional phone system with one that works entirely over Internet Protocol networks.

AT&T has argued that the technology transition should be accompanied by deregulation that would strip the company of most of its monopoly-era obligations. AT&T likely won't get everything it wants, though. FCC Chairman Tom Wheeler wrote in a blog post last November that he intends to "ensure the continuation of the Network Compact" with universal service for all Americans, consumer protections, public safety services, and competition.

In other words, AT&T can't stop maintaining the Public Switched Telephone Network (PSTN) without a plan to preserve current service levels. This is not as simple as just making sure phone calls get through, although solving the rural call completion problem by itself is a challenge. It also means maintaining access to 911 services, fire alarms, fax machines, medical alert systems, anything that relies on the phone network.

Not everything is to be decided this week. The FCC vote is on an AT&T petition to launch customer trials of new IP-based networks. While AT&T's petition is expected to be granted, the FCC's proposed order is written to ensure continuation of the four values (universal service, consumer protection, public safety, and competition) as Wheeler emphasized, an FCC official told Ars on condition that he not be named.

AT&T is "getting what they want. They're not getting it exactly the way they want it," Harold Feld, senior VP of consumer advocacy group Public Knowledge, told Ars. Feld has submitted filings in the FCC's IP transition proceeding.

The trials, Feld said, will provide the first real-world data needed to help the FCC set baseline technical standards that carriers would have to meet after the PSTN is shut off.

"In order to turn off the existing phone service you have to show that it's not going to impair service to the community," Feld said. "How do you measure that? The FCC doesn't have any measurements for that right now."

Ultimately, AT&T wants to move everything to IP and stop maintaining the PSTN by roughly 2020. In some areas where wired infrastructure is difficult to maintain, AT&T wants to deploy wireless-only services. The company did not provide any comment to Ars in advance of today's vote.

(UPDATE: As expected, The FCC today voted unanimously in favor of beginning the IP transition trials. After the vote, AT&T called it a "bold leap forward on the path to a modern 21st Century broadband world," and noted that "AT&T’s consumer POTS [plain old telephone service] access lines decreased from 15.7 to 12.4 million lines between 2012 and 2013.")

PSTN shutoff will be voluntary—at first

Feld laid out what's expected to happen today in a blog post:

The FCC will issue its first real full Commission action on the transition of the phone system. The FCC will adopt a set of principles to provide a framework for the transition—something we’ve pushed the FCC to do for almost exactly a full year. Also as part of the item, the FCC will outline the process for AT&T (or any other carrier) to apply to conduct technical trials that will inform the transition. The contentious issue that may split the FCC along party lines is whether participation in a technical trial should be mandatory for all consumers and businesses in the selected geographic area, or whether participation in technical trials will require consumers and businesses to consent to participate. PK has pushed very hard that “consumers are not guinea pigs” and participation should be voluntary. At last report, Republican Commissioners disagree and want to require all businesses and consumers in the test area to participate. The item was written before the network neutrality decision. So even though the network neutrality decision will have a big impact on the transition overall, I don’t expect any of the Commissioners to talk about it at this meeting. But they might.

The FCC official who spoke with Ars said the proposal under discussion would separate the trials into three stages and make the first stage voluntary. In first-stage trials, carriers would be permitted to offer an all-IP service but couldn't force existing customers to give up their current phone service (something Verizon tried to do in hurricane-ravaged Fire Island until backing down in the face of regulatory pressure).

In second-stage trials, carriers could ask the FCC for permission to move all customers in the trial area onto an IP-based service. In a third stage, the carrier would no longer have to maintain the PSTN in the trial area. No locations were mentioned, but the FCC would want geographic and demographic diversity, the FCC official said.

The type of technology used would be up to the carrier. In rural areas where it's expensive to wire up every home, carriers might try to shift everyone to wireless service. AT&T has said that in 25 percent of its customer locations, "it's currently not economically feasible to build a competitive IP wireline network," so it would use 4G LTE instead "to offer voice and high-speed IP Internet services."

There will be concerns about reliability of wireless services, particularly during power outages, but the FCC official said Wheeler isn't reflexively for or against wireless as a replacement for the PSTN.

The first trials could be greenlighted by the FCC as early as May. AT&T is likely to be the first to request permission to start trials, but there won't be any deadline preventing other carriers from starting trials later.

In addition to the trials, the FCC is expected to vote on funding research and development to improve access for people with disabilities and on a proposal to boost broadband access in rural areas.