(3) the secondary transmission is made by any carrier who has no direct or indirect control over the content or selection of the primary transmission or over the particular recipients of the secondary transmission, and whose activities with respect to the secondary transmission consist solely of providing wires, cables, or other communications channels for the use of others: Provided, That the provisions of this paragraph extend only to the activities of said carrier with respect to secondary transmissions and do not exempt from liability the activities of others with respect to their own primary or secondary transmissions;