Wireless carriers must allow subscribers from other carriers to roam onto their high-speed mobile data networks, the FCC ruled today in a controversial vote split along party lines that could have an indirect impact on a couple of key issues associated with proposed 700 MHz LTE networks for first responders.

Under the FCC order, facilities-based wireless carriers must reach data roaming agreements with other facilities-based wireless carriers at “commercially reasonable terms” that allow consumers to use mobile data devices outside the network footprint of the subscriber’s service provider. Such roaming arrangements have been commonplace for years for mobile voice services, but they have been rare in the mobile-data arena.

FCC Chairman Julius Genachowski said the agency’s rules for voice roaming have been an “unbridled success,” noting that approving rules for mobile-data broadband services represents a “simple, logical step of extending the basic roaming framework.” Without such rules — or even the threat that the FCC might create them — Verizon and AT&T have been slow to reach data-roaming agreements with competitors, he said.

Fellow Democratic commissioners Michael Copps and Mignon Clyburn applauded the mobile-data roaming proposal, noting that consumers expect to use their mobile-data devices — smartphones, tablets or laptop computers — wherever they are located, regardless of their carrier’s network footprint. By requiring wireless giants such as Verizon and AT&T to provide data roaming agreements, smaller carriers have an avenue to provide nationwide data coverage needed to give consumers competitive marketplace choices.

“I’m very pleased that data roaming’s time has arrived,” Copps said, noting the benefits that roaming provides to consumers and competitive wireless carries. “It’s what we should be doing, and I’m glad it’s what we are doing.”

But Republican commissioners Robert McDowell and Meredith Attwell Baker said the FCC lacks the legal authority to implement such rules, claiming that they essentially represent a common-carrier obligation by mandating that carriers agree to data-roaming deals. Under Section 332(c)(2) of the Communications Act, “a private mobile service [like data roaming] shall not … be treated as a common carrier for any purpose,” Baker said.

But Genachowski said the new FCC rules are “the very opposite of common carriage,” because the rules do not dictate roaming rates. If carriers are unable to reach a business arrangement regarding the rates or other terms of access, the FCC will decide disputes while following a “baseball-style” arbitration process, Genachowski said.

McDowell disagreed that the absence of predetermined rates would mean that the data-roaming mandate effectively is common carriage.

“We cannot evade the law by upending years of legal precedent and congressional intent to recast and redefine the meaning of common carriage,” he said.

If the FCC order remains in place, it could weaken the argument that the 700 MHz D Block should be auctioned to commercial operators, said mobile wireless consultant Andrew Seybold, who noted that “mobile data roaming is much more complicated that voice roaming” for a carrier.

Under the FCC order, carriers are not required to have any specific infrastructure or spectrum for their customers to roam onto LTE networks, FCC spokesman Rob Kenny said.

Seybold said that one reason T-Mobile officials — prior to the company’s merger announcement with AT&T—wanted the D Block to be auctioned was because they wanted 700 MHz spectrum, because there was a belief that a carrier would have to have a 4G network for the FCC to require AT&T and Verizon to cut a roaming deal with another carrier.

“[T-Mobile representatives] said they needed the D Block to convince the FCC to require AT&T and Verizon to let them roam on the AT&T and Verizon LTE networks,” Seybold said. “What this means is that one of the reasons that everybody was fighting for the D Block auction just crumbled away.”

AT&T and Verizon have long expressed interest in pursuing data roaming agreements with public-safety agencies, so personnel can use mobile-data technology when they are outside the range of their private broadband networks, such as the proposed 700 MHz LTE systems for first responders. Seybold said he does not believe the FCC order will have much impact on carriers’ willingness to let public safety access their networks, but a data-roaming mandate could result in technical work associated with roaming between networks will be accelerated.