If there's interest in this kind of stuff, I'm working on open-sourcing the core of a SaaS side project[0] I have. It's visual voicemail on steroids (cliché, sorry) and, like the linked article describes, accepts your forwarded call and handles the voicemail. Afterwards (and this was my original use-case), it can trigger a bunch of hooks to your favorite things — Dropbox, email, Slack, SMS, Zapier, what have you (and all right out of the box).
I built it because I was on Android and wanted to keep my moms voicemails. :)