Just like Verizon did last week, T-Mobile has submitted an amicus curiae to the court, officially siding with Samsung in its ongoing litigation against Apple. For the non-lawyers, an amicus curiae is when someone volunteers to offer information to assist a court in deciding on an issue.
T-Mobile's argument is similar to Verizon's. Both company don't want to see any of their best-selling 4G devices banned during the holiday season. Obviously, it would be a huge loss for the carriers, who generate a big chunk of revenue from this time of the year...