The rules in this subpart F apply to:

(a) A person engaged in the business of manufacturing, importing, selling, or leasing multi-line telephone systems;

(b) A person engaged in the business of installing, managing, or operating multi-line telephone systems;

(c) Any multi-line telephone system that is manufactured, imported, offered for first sale or lease, first sold or leased, or installed after February 16, 2020.