it's not transmitting anything and thus the FCC does not apply
If it's preventing reception of phone calls and it is a device (it is and it is) from a very, very cursory reading of the act, I think we have a problem. See Title III, Part I, Secs 301, 302, paragraphs (a)-(c) (p. 137-8), Sec 333 (p.183), and Title V, Secs 501-2 (p. 240-1). Related: Sec 706, p 323, paragraphs (b) and (h).
For fun, check out Sec 508 (p. 246). "Quiz Show" anyone?
I am not a lawyer; this is just a layman's interpretation of a quick reading of various paragraphs of the act.