US Code, Title 13, Chapter 7, Subchapter II, § 221 outlines the penalties:
(a) Whoever, being over eighteen years of age, refuses or
willfully neglects, when requested by the Secretary, or by any
other authorized officer or employee of the Department of Commerce
or bureau or agency thereof acting under the instructions of the
Secretary or authorized officer, to answer, to the best of his
knowledge, any of the questions on any schedule submitted to him in
connection with any census or survey provided for by subchapters I,
II, IV, and V of chapter 5 of this title, applying to himself or to
the family to which he belongs or is related, or to the farm or
farms of which he or his family is the occupant, shall be fined not
more than
$100 (emphasis added).
(b) Whoever, when answering questions described in subsection (a)
of this section, and under the conditions or circumstances
described in such subsection, willfully gives any answer that is
false, shall be fined not more than
$500 (emphasis added).
(c) Notwithstanding any other provision of this title, no person
shall be compelled to disclose information relative to his
religious beliefs or to membership in a religious body.
So $100 for not giving your phone number, $500 for intentionally giving a wrong number. No mention of jail time.
I guess one must return the census stating only the number of persons in residence (nothing else) along with an affidavit that other information is intentionally omitted. Copy info to major media. Take your $100 hit, then sue the Census bureau and hope you get your $100 back by order of the Supreme Court (I'd frame that check!).
Otherwise, you're probably stuck doing what I'm going to do... fill it out completely and truthfully. At least my clan will get counted for congressional representation purposes. I certainly don't have the 'nads to slug it out with the man!
Jack