The Western Trust spent £3,239,000 on phone bills between 2011/12 and 2013/14.
However, the health authority managed to reduced the charged over the same three year period.
The Health Minister Simon Hamilton revealed the level of expenditure in response to an Assembly Question.
The bill fell from £1,195,000 in 2011/12; to £1,050,000 in 2012/13; and further to £994,000 in 2013/14.
The Minister did not break down how the money was spent across the Western Trust estate by location, speciality or services.