I see where the FCC rules tell the manufacturers to afix that label. But I don't see where the modification of a radio set is actually illegal. It is certainly vague with respect to an individual making modifications. I read 15.121 through a couple of times; it is a strange requirement about that label. Clearly, manufacturing a radio to receive cellular signals is illegal. And it's clear that if you modify one, you can't sell it: section 2(d). Only in section 2(b) is there a hint that having such a radio might be illegal: "Except as provided in paragraph (c) of this section, scanning receivers shall reject any signals..."