Mr Hallenstein, of Melbourne, fought in places including Gallipoli and France and sent letters from the front to his family and friends.
''It is his life in the trenches,'' Mr Flaherty said.
The Hallenstein family published the letters after their son was killed in the war.
Mr Flaherty will read the letters in a weekly radio series on Otago Access Radio called War Stories from the Olveston Library.
The book of letters was one of nearly 2000 in the Olveston library and was inscribed to the original owners of the house, David and Marie Theomin, who were relations of the Hallensteins.
Mr and Mrs Theomin's son Edward was mentioned in the letters, Mr Flaherty said.
The first of the weekly half-hour programmes begins at 12.30pm today, and continues for 26 weeks.
It will include wartime music and poetry.
