Total posts : 45366
It is not legal to use a 100 mw FM transmitter, certified or not without a license. Current the FCC does not license any FM operating below 100 watts.
As far as AM, 100 mw is legal certified or not. One may not sell a pre-assembled AM transmitter without it being certified. Kits or home brew OK as long as the power does not exceed 100 mw and the combined length of antenna and ground lead do not exceed 3 meters.