WOW, nice find!
The best part: Sanity is a free software, opensource, released under GNU Public License version 3. I mean, for handling calls & SMS I don't trust closed software (for privacy matters).
One suggestion (if the programmer is reading this): add a basic "IVR" option (with a custom voicemail), and this will be just PERFECT!. What's IVR? It's an interactive voice menu, but it's not so hard to implement it, since it's only a recording (that the user needs to record), asking callers to enter an "extension" number. If that extension number matches, the phone would ring. This can be applied to all numbers, or only to numbers that are not in our phone book. For example: "Hello, this is John's phone!, if you know the extension number, please enter it after the beep, or press 9 to leave a message.". For the voicemail, the message is saved in MP3, so you don't have to use you carrier voicemail. Just PERFECT!
If you need more explanations, just ask.
I will test it, in a few days...
Thanks for sharing!