Sorry I missed this one in my previous post. To answer you, obviously, it doesn't explicitly say it anywhere in the Constitution, because of course, the Founding Fathers could never have envisioned radio back in 1787! But for better or worse (mostly worse), the "necessary and proper" clause has been interpreted to cover a whole lot of regulations, the FCC among them. Because someone determined that the FCC was "necessary and proper" to ensure decency standards on the public ariwaves, the three pronged test was created, and is at long last being enforced against the likes of Stern, Bubba, et al. I'd much rather Cheap Channel, Citadel, Infinity and the few other remaining radio groups enforce the standards themselves, but if they don't, I say sue 'em into oblivion.
Scouts Out! Cavalry Ho!