5D - Bill's comment about phony diamonds (6) - N?T?C?
Note the less common spelling of "phony" in the clue. For this I have put NOTACE, which I get from NOTE (comment) about AC (bill), but I can't find any definition of that word relating to phoney (or phony) diamonds. It seems to be a Czechoslovakian prefix! An alternative solution is NOTICE (bil?), built from NOT + ICE (diamonds), but the NOT part doesn't make sense.
Any offers of other solutions?