Are polyatomic ions ionic?

$\text{Sulfates, nitrates, perchlorates, phosphates.......}$; all of these species, and others, are polyatomic ions. Lewis structures can represent (sometimes) their ionic character: O=N^(+)(-O)_2""^-, (O=)_2S(-O)_2^-,(O=)_3ClO^(-); all of these species have formal negative charges. And these are combined with metal or protic cations in the solid state. And of course, cations, too, can be polyatomic; the best example is $\text{ammonium ion}$, i.e. $N {H}_{4}^{+}$.