The main concern about boosters is that they interfere with signals from cell towers on the same frequencies. Wilson, a manufacturer in St. George, Utah, that makes boosters that work with multiple carriers' phones, has been asking the FCC to regulate the devices since 2007. The company has said its products coexist well with carrier networks while some others may not.

Boosters do receive basic approval from the FCC as wireless devices. On Monday, the agency approved Wilson's first LTE booster for use in cars, Banos said. The product, called the Sleek 4G-V, can amplify Verizon LTE signals as well as 3G networks from the major carriers on the 800MHz and 1900MHz bands, Banos said. It should begin shipping immediately from retailers for an estimated US$129, the company said. Wilson is also developing a five-band booster for use with more carriers' networks, he said.

Wilson estimates that its unit sales of the products each month are in five figures. Some U.S. carriers, including Verizon and Sprint, offer subscribers femtocells, which act as small, indoor base stations. Femtocells differ from boosters in that they use the subscriber's own wired broadband connection as backhaul. And unlike some boosters, femtocells only work with devices from one carrier. By contrast, most of Wilson's boosters can serve all members of a household no matter what carrier they use, he said.

But possibly the most important role for boosters is coverage inside cars and trucks, for which femtocells aren't available. Wilson sells a majority of its devices for use in vehicles, Banos said.

If the FCC votes to require a carrier's permission to use a booster, the effects will depend partly on how a carrier can justify denying those requests, said analyst Peter Jarich of Current Analysis. If the carrier could do so for any reason, that might be bad news for third-party manufacturers. If they had to give a sound justification, the veto would matter less.