Income tax: is a Police Officer entitled to a deduction for costs incurred in maintaining a 'silent' telephone number?

No. This expenditure does not meet the requirements of subsection 51(1) of the Income Tax Assessment Act 1936. It is not incurred in gaining or producing the officer's assessable income. As the expense relates to a decision, the effect of which is to preserve anonymity and privacy, the outgoing is additionally private in nature.