Well, one easy way is to just call into the auto attendant and if they have a different greeting then they would hear that greeting. If not, then options are putting a key on phone using Status Groups for that system mode. Other option if setting up an option via the auto attendant to go to system mode and from there they can hear what status it is in but that does give them the ability to change it also from there.
Hope that helps. Let me know if you have any other questions.