UK mobile phone maker Sendo has launched legal action against Orange in the UK, claiming the operator has broken one of its patents.
The phone at the centre of the row
The row centres on the Orange SPV smartphone, which was launched in November last year and was the first mobile phone to carry a Microsoft operating system.
Sendo said the phone infringed a patent it had been granted relating to the design of the circuit board within the phone.
In reply, Orange said it "strongly denied" any wrongdoing.
"Sendo has created intellectual property rights within the smartphone and mobile phone area," Sendo's chief executive Hugh Brogan said in a statement.
Orange strongly denies any impropriety regarding the intellectual property rights of the SPV
"We have been advised by our patent agents that the Orange SPV phone infringes these rights."
Mr Brogan said the firm had tried to resolve the matter in an amicable way but it had decided it had to take legal action.
"We are seeking damages and an injunction to restrain sales of the product," he said.
"As we have previously stated, if Sendo believes that its global intellectual property rights are infringed, wherever in the world this might be, we will take steps to defend those rights."
"Orange is aware of the legal proceedings initiated by Sendo in the UK," Orange said in a statement.
"Clearly, Orange strongly denies any impropriety regarding the intellectual property rights of the SPV and has contacted the parties involved in the design and build of the handset.
"For legal reasons, we cannot comment any further."
The Orange SPV phone is manufactured by Taiwan's High Tech Computer (HTC).
Last December, Sendo started separate legal action against Microsoft alleging that the software giant was stealing its technology.
The legal action came after the two firms ditched an agreement to jointly develop multimedia mobile devices.
Sendo switched to Nokia as a technology partner, after fears that Microsoft was passing its intellectual property on to rival mobile makers.
Microsoft rejected the accusation.
A hearing on the case is due to take place in early July.