Mobile carrier AT&T has been criticised for making some Android phones appear to use 5G services, even though they are not widely available.
A software update issued by AT&T means icons used to display a connection's status will, in some situations, suggest a handset is on a 5G network.
Instead of being true 5G, the phones are using add-ons to existing 4G technology that seek to boost speeds.
AT&T said the move was "laying the foundation" for the move to 5G.
Rival T-Mobile responded via Twitter with a video showing someone putting a 9G sticker on their phone screen.
The T-Mobile tweet mocked AT&T saying it "didn't realise it was this easy, brb updating".
Verizon said it would not be following AT&T's lead, reported The Verge.
AT&T said it planned to introduce "standards-based" 5G widely in 2019, when more fully 5G-capable phones become available. Currently 5G services from AT&T are only available in six big US cities.
On phones, true 5G will denoted by an icon displaying "5G+".
By contrast, the controversial update being rolled out now will use a "5GE" icon to denote that a device is actually using so-called "evolutionary" technologies for existing 4G networks.
The 5GE technologies will be available in 400 towns and cities, said AT&T, and should provide a boost to browsing speeds at some times.
A total of 17 Android models are affected by the update, said Kevin Petersen, senior vice-president of device and network experiences, in a blog. One Samsung and two LG phones will be the first to see the update with other Android handsets following in the spring.
He said the icon change was part of its "path to 5G" and would help prepare people for the shift to the newer technology.
Writing on the Ars Technica news site, Ron Amadeo called the change "ridiculous" and said it could "mislead consumers".
Many other US networks using the same evolutionary add-ons for 4G have not changed the way they are represented on a phone display, said Mr Amadeo. Some carriers introduced the boost to 4G long before AT&T, he added.
He cautioned Americans against being an early adopter of 5G saying the roll-out was becoming a "huge mess".