In the letter from its lawyers, T-Mobile claims that sipgate is making the jailbreak process appear more attractive, which could lead customers to breaching their contracts.
According to Salmon, T-Mobile disallows jailbreaking, running VoIP, instant messaging, and VPN applications as part of its subscriber contract. Salmon notes, however, that sipgate only works via WiFi (and not GPRS or EDGE), and therefore does not run on T-Mobile's network. He says, "for the time being our users are safe."
sipgate doubts the legal veracity of the argument, and said it does not plan to comply with the order. Salmon said "we may need to fight this all the way through the courts." He also suggests that it's largely a government policy issue for Germany, and wants to lobby for a net-neutral environment for telecom carriers.