Do your research on Samsung as they are not pentaband phones even though the S5 is the flagship phone. Pentaband means they will work on most carriers broadcast frequencies (still check first, "http://www.gsmarena.com/ is a good way to start & Wikipedia will tell you what Australian carriers use which frequencies for mobile data. Samsung also have an octocore variant (8 core processor, "Galaxy S5 SM-G900i").
These are all the s5 carrier devices
Samsung SM-G900F/SM-G900H