Sprint is suing AT&T and claiming that the labeling of its 4G-Advanced services as "5G E" on many 4G smartphones is "deceptive."

Sprint Corp. (NYSE: S) filed a complaint against AT&T Inc. (NYSE: T) Thursday evening with the New York State Southern District court accusing AT&T of "deceptive advertising" over the "5G Evolution" service.

"AT&T has employed numerous deceptive tactics to mislead consumers into believing that it currently offers a coveted and highly anticipated fifth-generation wireless network, known as 5G," Sprint said in the complaint. "What AT&T touts as 5G, however, is nothing more than an enhanced fourth-generation Long Term Evolution wireless service, known as 4G LTE Advanced, which is offered by all other major wireless carriers."

The crux of the issue, Sprint notes, is that AT&T used a "software update to change the screens of mobile phones and tablets operating on the AT&T 4G LTE Advanced network to indicate falsely that these devices are connected to a 5G network."

AT&T offers a number of modern Apple and Samsung smartphones that display the "5G E" branding on screen when using LTE-A connections.

AT&T's CEO responded on CNBC's Squawk Box show Friday that the AT&T offering is evolutionary but not deceptive. "We're being very clear with our customers that this is an evolutionary step." Randall Stephenson said. (AT&T executives have also previously defended the marketing, see AT&T's Donovan Defends the Carrier's 5G Fibs.)

Rival carriers have also widely panned AT&T's move. (See Verizon, AT&T Spar Over 5G Service Names, Marketing.)

The kerfuffle over the "5G E" branding initially started in the press back in January. AT&T, however, started updating a planned 400 4G markets as with LTE Advanced upgrades, such as updated antenna arrays back in April 2018. (See AT&T Rolls Out Faux 5G in 100+ US Markets.)

Sprint is seeking to block AT&T from using "5G E" or other related terms with this complaint.

— Dan Jones, Mobile Editor, Light Reading