The *78 feature should override this permanent diversion, and an incoming call to the landline phone should be immediately bypassed without ringing (or perhaps ring once, like it used to do before NBN) and diverted to the mobile and ring long enough (more than the default 6-8 secs) to be picked up by the recipient or picked up by the mobile's ...
The most professional voicemail message should include a formal tone and specific instructions. For example, you may say “Hello, you’ve reached [your name], [job title] at [business name]. I’m sorry to have missed your call. Please leave your name, contact information, and reason for calling so I can get back to you promptly.”

If your carrier supports the iPhone voicemail feature, you can retrieve and listen to your voicemail right from within the “Phone” app and call your contacts back by simply tapping their messages. That type of functionality is pretty neat and useful, because it saves you actual time. If not supported by your carrier, you will not be able to see the visual overview of your voicemail inbox and use any of the related features. Tapping the “Voicemail” tab in your “Phone” app will simply call the number associated with your voicemail box. So let’s get going with creating our custom voicemail greeting on iPhone! How to record your own Voicemail on iPhone Phone → Voicemail → Greeting → Custom → Record → Save
Open your phone’s voicemail app, then tap (or in some cases, tap and hold) the message you want to save. You should be presented with a list of options; the save option will usually be listed as “save”, “save to phone,” “archive,” or something similar.