Apple has long made the processors that act as the brains of its iPhones, but the company has relied on Qualcomm's modems to connect its devices to cell networks.
From the iPhone 4S in 2011 to the iPhone X in 2017, Qualcomm was the sole provider of 4G chips that helped Apple's devices access Verizon, AT&T and other wireless services.
Because Qualcomm owns patents related to 3G, 4G and 5G phones -- as well as other features like software -- any handset makers building a device that connects to a network have to pay it a licensing fee, even if they don't use Qualcomm's chips.
When it filed its lawsuit two years ago, Apple asked the court to lower the amount it pays Qualcomm in licensing fees.
The US Federal Trade Commission sided with Apple and filed an antitrust lawsuit two years ago, accusing Qualcomm of operating a monopoly, requiring exclusive agreements and charging excessive licensing fees for its technology.