See as you are in sort of interdisciplinary field i.e., you do the data management and software development for the purpose of telecommunication then you should mention IT because you are not directly involved in Telecommunication as it would have been the case for any Electronics and Communication Engineer. So the wiser way would be to mention both or you may mentioned Telecommunication (Your job description in short).

I hope this answer helps. All the very best for your future endeavors!