AT&T was sued for $1.35 billion by Seattle-based Network Apps that accused the telecommunications giant of stealing its “twinning” technology.

Network Apps’ patented “twinning” technology lets smart devices such as watches and tablets respond to calls placed to a single phone number.

Network Apps said AT&T abandoned joint development and licensing agreements for its technology in 2014 after realizing it would owe a “fortune” in royalties because the market for smart devices was exploding, only to then incorporate the technology a year later in its own product, NumberSync.

According to a complaint filed in Manhattan federal court, NumberSync uses the “same concept and architecture” with only “cosmetic changes,” and its purported “inventors” were the same AT&T personnel who had worked with the plaintiffs.

Network Apps, which was once known as Mya Number, said Dallas-based AT&T has not paid required royalties since October 2015.

It is seeking at least $450 million of damages, which it wants tripled to reflect AT&T’s alleged “willful and egregious infringement,” plus royalties for any future infringements.

AT&T said it will review the lawsuit and respond in court.

Network Apps’ founders, John Wantz and Kyle Schei, in a joint statement said “AT&T’s decision to steal our technology” has forced them to scale back operations significantly. “Our technology is an eloquent solution for a critical problem at a critical time in the industry.”

According to AT&T’s website, NumberSync lets consumers make and receive calls on smartwatches, tablets, computers and compatible Alexa-enabled devices without having to download appsor engage in call-forwarding acrobatics.