Qualcomm is a major supplier to both Apple and Samsung Electronics Co Ltd for "modem" chips that connect phones to wireless networks. The two companies together accounted for 40 percent of Qualcomm's $23.5 billion in revenue in its most recent fiscal year. In the lawsuit filed in U.S. District Court for the Southern District of California, Apple accused Qualcomm of overcharging for chips and refusing to pay some $1 billion in promised rebates.