This made my head hurt, so I hope it’s useful!

 =IF(AND(A1>=2000,A1<=2599),"NSW", IF(AND(A1>=2619,A1<=2898),"NSW", IF(AND(A1>=2921,A1<=2999),"NSW", IF(AND(A1>=0200,A1<=0299),"ACT", IF(AND(A1>=2900,A1<=2920),"ACT", IF(AND(A1>=2600,A1<=2618),"ACT", IF(AND(A1>=3000,A1<=3999),"VIC", IF(AND(A1>=8000,A1<=8999),"VIC", IF(AND(A1>=4000,A1<=4999),"QLD", IF(AND(A1>=9000,A1<=9999),"QLD", IF(AND(A1>=5000,A1<=5999),"SA", IF(AND(A1>=6000,A1<=6999),"WA", IF(AND(A1>=7000,A1<=7999),"TAS", IF(AND(A1>=0800,A1<=0999),"NT", "INT"))))))))))))))