Customise voicemail message based on caller

Is it possible to programme a specific voicemail message to be used when an individual telephone number calls me? I would like to have my general voicemail message for all calls except one from a client with dementia who needs a difference message to reassure her.

I am using an iPhone 6 running iOS 12.

Voicemail is a carrier feature and currently, there are no carriers as far as I am aware that permit you to store multiple greetings.

Reference: https://discussions.apple.com/thread/3841850?answerId=3841850021#3841850021

Voicemail is a carrier feature & your greeting is stored on their servers. I'm not aware of any carrier, anywhere, that permits multiple greetings.

The only option that I have used for this is Google Voice, which is free (I believe it’s only available in the USA). You can definitely make different voicemails for different groups (and put just one person in a group if you want).

Thanks to a comment by @MonkeyZeus, according to http://itstillworks.com/forward-voicemail-google-voice-5795554.html you can forward your regular number to Google Voice so that your contacts never interact with the Google Voice number.

There is no way to do this directly from within iOS as voicemails are generally a service provided by the phone network.

However, there are a number of 3rd party services (e.g. You Mail) you can subscribe to that claim to offer this functionality.

Unfortunately, I haven't used any of these services so cannot attest to how well they work or not.