> You cannot argue for Common Carrier status in front of a judge if you're not classified as a common carrier by the FCC.

Sure you can, since “common carrier” is a centuries old common law classification that the FCC has nothing to do with, as well as also a statutory classification under the Telecommunication Act inspired by the common law classification, as well as a statutory classification under other laws.

And even for the classification under the Telecommunication Act, one could argue the definition in the Act whether or not the FCC has applied it in a particular way (this requires overcoming the deference that courts give to executive agencies delegated decision-making powers by Congress, but it is not an impossible argument to make in principle.)