If you are taxiing at an unmarked aerodrome near a frequency boundary ( like Wilpena) you give the taxiing calls on both ATC area frequencies
Well how else would anyone else in the vicinity become aware of your intentions? You are at an unmarked strip. Nobody is going to anticipate you popping up in front of them if they don't know an aerodrome is there. That's what an Area Frequency is for, ffs.