Sim cards very cheap , pulsa (prepaid credit various amounts) sms to australia cost approx 600 rupiah for simpati , dearest to use but best coverage , calls home can be cheap ask for code to use with your sim when calling home if use code 10000 rupiah maybe get you 10 minits if no code 5 minits will cost you about 50000 . Locked Phones are not a problem you can always find someone to unlock for about 250,000 . if buying a phone go into denpasar for the cheapest deals stay away from the tourists spots or you pay more simple as that . Hope this helps