Downloading voicemails

I like to have all my important voicemails backed up to my own computer. As smarty doesn’t have visual voicemail I can’t export it like normal. Does anyone know how they can be downloaded? 

I found this pdf which talks about getting them forwarded by email which I could then download but I don’t know if it’s a red herring https://www.three.ie/content/dam/3ie-wotf/pdfs/business/3connect/three-business-3connect-managing-voicemail-user-guide.pdf 

thanks in advance 🙂