AT&T said that it could use its extensive millimeter wave (mmWave) spectrum holdings for both fixed and mobile 5G services. The company's announcement is the first hint at AT&T's possible plans for the $2 billion worth of highband, mmWave spectrum it purchased in FCC auctions over the past year.

"Once the network is built with the necessary density for mobile services, fixed services may follow," AT&T said Tuesday in a brief release about its mmWave spectrum purchases.

The carrier boasted that it now owns roughly 1,040MHz of mmWave spectrum nationwide.

To be clear, AT&T has already dabbled in offering fixed wireless services across a range of different spectrum bands, including mmWave bands. However, the carrier hasn't formed a clear business around the technology like Verizon has with its 5G Home fixed wireless service.

Verizon, for its part, intends to offer 5G Home fixed wireless services to up to 30 million US households within the next five to seven years, but its 5G Home buildout has stuttered through a number of market tests as Verizon refines the equipment and installation technique for the offering.

Importantly, Verizon has said that it expects to begin expanding 5G Home to more customers later this year. It's waiting to obtain new chipsets from Qualcomm that can boost transmissions from customers' equipment, thus expanding the range of Verizon's fixed wireless service.

Fixed wireless services from the likes of Verizon and AT&T would represent a challenge to wired Internet providers like Comcast, CenturyLink and others.

AT&T, for its part, has so far shied away from providing many specifics about its mmWave network buildout plans. The company now offers commercial, mobile mmWave services in parts of 35 US cities – AT&T calls the offering "5G+," thereby marking it as different from the "5G" service the carrier is providing in its lowband spectrum holdings.

But AT&T so far has made no firm promises to expand its mmWave "5G+" network to additional cities. AT&T's silence on the topic is particularly deafening considering Verizon announced earlier this year it would double the number of cities where it is offering mobile mmWave 5G service – from around 30 cities currently to around 60 by the end of this year.

That said, AT&T clearly has mmWave ambitions, given the roughly $2.2 billion it has spent on mmWave spectrum licenses in recent FCC auctions. The company dropped $982 million on licenses during the FCC's Auction 102 of 24GHz licenses that ended last year, and then doled out another $1.2 billion on more mmWave licenses during the FCC's Auction 103 of 37GHz, 39GHz and 47GHz licenses that ended earlier this year. And all that mmWave spectrum sits next to the 39GHz licenses AT&T purchased from FiberTower in early 2018.

"With this newly acquired spectrum and our existing holdings, AT&T continues to build upon and add capacity to the nation's largest network," AT&T said Tuesday in its release.

While mmWave spectrum promises to support blistering-fast speeds of up to 4Gbit/s, the technology is very difficult to deploy on a widespread basis because signals in mmWave spectrum can only travel a few thousand feet in the best of conditions. That has forced operators like AT&T and Verizon to begin installing hundreds of thousands of small cell transmitters atop light poles, rooftops and other structures, in order to move their 5G broadcasts closer to customers. Although new FCC rules are geared toward making it easier for carriers and others to deploy those small cells, cities around the country continue to move slowly in providing necessary approvals for the gadgets.

— Mike Dano, Editorial Director, 5G & Mobile Strategies, Light Reading | @mikeddano