Some AT&T customers with iPhones noticed something weird earlier this week. Those who had installed a new beta version of iOS reported seeing "5GE," rather than "4G" or "LTE," in the upper right-hand corner of their screens, according to The Verge. But Apple doesn't sell an iPhone that supports 5G standards, and AT&T doesn't yet offer 5G service for mobile phones.

In fact, what those customers saw was a bit of AT&T marketing. AT&T has branded parts of its 4G network as 5GE, or "5G Evolution." Apple has apparently added that branding to the latest version of its mobile operating system, but doesn't mean that anyone's connection is actually faster because of it.

AT&T drew criticism from competitors that offer the same network technologies. Now, Sprint is suing AT&T, arguing that its advertising is deceptive. "It harms consumers by holding out AT&T’s services as more technologically advanced than Sprint’s and enticing consumers to switch wireless service providers (or remain AT&T subscribers) under false pretenses," the lawsuit, which was filed Thursday and spotted by Engadget, says.

Sprint declined to comment on whether it would add other defendants to the suit, such as Samsung, which also displays the 5GE branding on some phones on AT&T networks, or Apple.

Someday real 5G networks could enable mobile speeds of around 10 gigabits per second---about 10 times faster than the standard Google Fiber connection. But AT&T's Evolution service, which it introduced in 2017, doesn't deliver speeds anywhere near that fast. The company claims the service has a theoretical upper limit of more than 400 megabits per second. Even the few services based on actual 5G technologies today can't top 1 gigabit per second. Nationwide 5G networks aren't expected until 2020, and few phones available today can support 5G.

AT&T argues that consumers know the difference between its "5GE" offering and actual 5G. "We introduced 5G Evolution more than two years ago, clearly defining it as an evolutionary step to standards-based 5G," an AT&T spokesperson said in a statement. "5G Evolution and the 5GE indicator simply let customers know when their device is in an area where speeds up to twice as fast as standard LTE are available."

Whether customers can discern the difference will be the heart of the lawsuit, says H. Jonathan Redway, an attorney at Dickinson Wright with a background in false advertising cases. If AT&T loses, it might have to pay Sprint for lost customers and also shell out for an advertising campaign to correct the record.

The suit may be a bit of marketing on Sprint’s part, but it also underscores how confusing terms like 4G and 5G are for consumers.

LEARN MORE The WIRED Guide to 5G

"When one carrier starts suing another carrier over 5G claims, it's a sign that the 'race to 5G' marketing campaign is getting out of hand," Chris Lewis, president of the advocacy group Public Knowledge, said in a statement. "Communities want to know exactly what they are getting from their carriers. It is important that all carriers are giving clear expectations to consumers about what 5G is, what it enables, and most importantly, what communities will or won't benefit from it."

Part of the problem is that the terms 4G and 5G are nebulous. Neither refers to a specific technology. They're umbrella terms for a number of different technologies and standards used to build successive "generations" of wireless networks.

The four largest US mobile carriers have largely settled on the LTE, or "Long Term Evolution" standard for their 4G networks. AT&T's "5G Evolution" is the company's name for the newer "LTE Advanced" standard. All four major carriers now support LTE Advanced, but only AT&T calls it 5G Evolution.

Carriers have a history of playing these sorts of word games. For example, HSPA+ is an enhanced version of the 3G standard HSPA. Before it had a nationwide LTE network, T-Mobile advertised its HSPA+ network as "4G speed" until the International Telecommunications Union, a United Nations agency that handles standards, allowed carriers to label HSPA+ networks as "4G." At that point T-Mobile dropped the "speed" part and began advertising its network as 4G, as did AT&T. In a recent blog post, T-Mobile CEO John Legere called AT&T’s 5GE “BS,” and said AT&T is “lying to their customers.” He said AT&T’s tactics differ from what T-Mobile did with HSPA+ because the ITU hasn't signed off on calling LTE Evolution "5G." The ITU didn't respond to a request for comment.