(Adds details on InterDigital's patent cases, share price)
WASHINGTON, June 13 (Reuters) - Nokia Corp and ZTE Corp have not violated InterDigital Inc's patents for making wireless phones, a U.S. International Trade Commission judge said in a preliminary ruling released on Friday.
The full commission is expected to issue a final ruling in October.
InterDigital shares plunged on the ruling, and were down about 9 percent in U.S. afternoon trading.
Initially, Wilmington, Delaware-based InterDigital had also sued Samsung Electronics and Huawei for infringement but these two companies opted to settle.
It had accused the companies of infringing on seven patents when the case was filed in 2013, but four dropped out in the course of litigation.
The ITC is a popular venue for patent lawsuits because it can ban products that infringe on patents from being imported into the United States more easily than district courts can.