When a message is left with Apple Visual Voicemail, you'll see a notification against the phone icon on your iPhone.
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 ...

Most people screen their phone calls and often avoid answering unknown numbers. If you’re applying for new positions, you should try to view each unexpected call as an exciting opportunity! In the event that you simply can’t pick up the phone, you’ll want a polished voicemail greeting to let the caller know they’ve reached the right person.
To enable Visual Voicemail, you must create a password by accessing your voicemail and then record a greeting as follows: Access the Telephone app, select the Voicemail tab and tap Configure now. Select a password for your voicemail and tap Done. Confirm your password by re-entering it and tap Done. Select Custom if you wish to save a new greeting or Default if you don’t wish to edit your message. Tap Save.