The best open source alternative to Google Voice is Nertivia, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Google Voice and three of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Google Voice are JMP.chat (Paid, Open Source) and Jingle (Free, Open Source).
Nertivia is an chat client that allows you to chat to anyone across the world. There are a lot of features that don't require you to pay at all such as, gif profile pictures, free custom emojis and more coming soon!
No screenshots yet
Nertivia vs Google Voice opinions
pros, cons and recent comments
It's a chat app, not a virtual phone number service.
is an extension to the Extensible Messaging and Presence Protocol (XMPP) which adds peer-to-peer (P2P) session control (signaling) for multimedia interactions such as in Voice over IP (VoIP) or videoconferencing communications.