Huawei Technologies and ZTE may be opponents in a series of 4G technology patent disputes in European courts, but China's two biggest telecommunications equipment manufacturers have closed ranks to fight intellectual property cases against them.
Their common foe in the two other high-profile lawsuits is InterDigital, a Philadelphia-based developer of wireless communications technologies used in mobile devices, networks and services worldwide.
Huawei, ZTE, Nokia and Samsung Electronics were accused by InterDigital of infringing certain 3G and 4G patents in a case it filed in January with the United States International Trade Commission (ITC).
InterDigital also filed a parallel lawsuit in the US District Court of Delaware, where it has sought a ban on the import of infringing 3G and 4G devices into the US market.
Over the past few months, the two Shenzhen-based telecommunications equipment makers have co-ordinated their efforts in both the ITC's investigation of InterDigital's complaint against them and the Delaware court case.
"We have this term, 'co-opetition', in our industry," Huawei spokesman Scott Sykes said.
Sykes said the two firms generally competed against each other, but must co-operate in certain matters like the InterDigital case.
Florian Mueller, an intellectual property analyst, said in his Foss Patents online report that Huawei and ZTE "present a united front against InterDigital, despite being embroiled in a standard essential patents dispute with each other in various jurisdictions".
While their combined resources against InterDigital may seem formidable, Huawei and ZTE were last month denied their joint motions to stay the ITC proceedings and to expedite the Delaware court's hearing.
InterDigital wanted the ITC case to go ahead without delay as part of its bid to win an import ban as quickly as possible, Mueller said.
Huawei and ZTE wanted the so-called frand licence determination in the Delaware court to happen first.
Frand, which is typically used to describe patent-licensing arrangements, is a legal term that stands for "fair, reasonable and non-discriminatory".
Last week, the Paris District Court ordered Huawei to pay €100,000 (HK$995,000) in damages to ZTE after dismissing Huawei's infringement complaint against Hong Kong-listed ZTE.
"The decision was within ZTE's expectations," Guo Xiaoming, the company's chief legal officer, said.
That followed the Dusseldorf Regional Court's decision two weeks ago that referred several questions related to Huawei's case against ZTE to the Court of Justice of the European Union in Luxembourg.