Mobile phone giant Vodafone has challenged T-Mobile's Apple iPhone deal, which ties iPhone buyers to the German firm's network for two years.
iPhone users are tied to one phone network
Vodafone has been granted a temporary injunction against T-Mobile, with a court hearing due to take place in Hamburg in two weeks time.
Vodafone says it does not want to stop T-Mobile selling the phone but wants customers to choose their own network.
Apple has faced criticism that iPhone users are tied to certain networks.
Free to choose?
Under German law, T-Mobile's iPhone distribution deal is uncompetitive, the Vodafone spokesman said.
"We believe that T-Mobile has breached a local law in Germany," a Vodafone spokesman told the BBC.
The computer giant rolled out the iPhone this year
The injunction does not mean that iPhone has to stop selling the phone, he added.
T Mobile said it is examining the injunction.
It is not unusual for mobile providers to have exclusive deals with phone firms, a spokesman added.
Same around the world
Apple's iPhone distribution deal with T-Mobile resembles iPhone deals around the world.
iPhone buyers in the US have to use AT&T, while UK users are tied to 02.
The phones can be unlocked for use on other networks but this voids the warranty and could break the device if software updates from Apple are installed.
As many as 250,000 users in the US have unlocked the device using free and paid-for software to make the phone work on different networks, and to load third-party software not supported by Apple.
Vodafone has no plans to take further injunctions against rivals selling the iPhone, a company spokesman said.