I originally didn't understand why OTIV was suing T-mobile, but now it is really clear. Why not sue the NFC chip maker or the handset maker? Because the carrier (in this case Tmobile, but ATT and Verizon are also in this partnership called ISIS) making the customer get a new SIM chip with the Secure Element ID to allow the ISIS app to send the credit card info through the NFC chip in the phone to the payment reception device.
The OTIV patent which describes this process is 13 years old and these carriers now want to implement the technology without paying for it. I think OTIV has a pretty good shot and if anything, they might put a halt to ISIS while it is in court which will cost these guys millions. The marksman was huge and T-mobile has a few days to decide what to do.