Motorola's persuaded an International Trade Commission (ITC) judge that Microsoft's Xbox 360 violates four of its patents - and is now pushing for an import ban.
Judge David Shaw yesterday ruled that the Xbox 360 infringed patents covering wireless networking and video coding, although he ruled in favour of Microsoft on a fifth.
Microsoft had claimed that Motorola was acting unreasonably by not licensing the technology under FRAND - fair, reasonable and non-discriminatory - terms. The EU is currently examining the same issues.
And the results of the EU case, says patent expert Florian Mueller, will be more influential than the ITC verdict.
"The opinion of one ITC judge on a FRAND defense is, in my opinion, far less meaningful than what federal courts and antitrust regulators say. Motorola is being formally investigated by the European Commission for suspected abuse of patents essential to particular standards that are also at issue in its ITC and other cases," he says.
"Even though the start of formal investigations doesn't constitute a final decision, it's based on reasonably strong suspicions of abuse - a fact that says more than an initial determination by the ITC, which is a trade body, not an antitrust enforcer."
Motorola's next task is to persuade a judge to order an import ban - potentially meaning that US residents won't be able to buy an Xbox 360 during the Christmas selling season. A more likely outcome is, finally, some sort of settlement between the two companies.
There'll be a full ruling in August.