hi guys,
no sure if it's a good idea and want some opinion, the only issue I can think of is charger, easy fix, just buy adapter, or just buy wireless charger in Australia, also no sure about gsm, is it just relating to mobile internet speed? any suggestion appreciated.
Go to http://www.willmyphonework.net/
I'm pretty sure this phone was made for AT&T (american provider) so it could be a locked device.
enter relavant information, it'll tell you if that specific model works with your chosen telco.
Remember that Samsung makes different models for different regions so it is possible that a Samsung S6 for example, can have multiple models within with very similar names.
GSM is a worldwide standard, but in Australia we use 3G UMTS / HSDPA and also 4G FDD LTE.
All the relevant 3G and 4G frequency bands in use in Australia is listed here
https://whirlpool.net.au/wiki/mobile_phone_frequencies