Sure, open source means everything you've mentioned. However, it largely depends on the usage license with which the software is initiated. Anyway, I don't see it being useful to pay for a startup that will eventually become a competitor to Vivox. I find a project in the style of FreeSWITCH more useful – open source – where, just like with OpenSimulator, anyone can download the code and reshape it to fit their needs. This would attract a large number of free and interested programmers, much like what happens with many Unix or GNU/Linux-based software.
The server wouldn't be centralized, but each user would have their own, independent from others. So, each grid would have its own voice server. This doesn't incur development costs because I can manage the repositories from my PC, make changes from my PC, and test the software on my PC without requiring sums like $60,000 – and this would be multiplied by the many contributing users. If someone is needed to do this, so be it.
If FreeSWITCH were simpler, it would be ideal to pursue that project. I tried to run it on a Windows server, but with very limited results. Adapting a voice service for viewers isn't simple, but in my opinion, the best solution remains starting with a solid open-source software under the GPL license, integrating the necessary modules (and if needed, moving towards LGPL). This way, everyone can host their own voice server on their machine, decentralized from the rest. Instead of giving money to a project that centralizes voice servers, it creates a completely different type of project and supports a startup that, no matter how open their code might be, aims to have control over the users of its services. OpenSimulator is not like this. If I had to choose, I'd prefer to pay for services from a company like Vivox; at least I know it's reputable and already present in various gaming services, including professional tournaments and Second Life.
However, fundamentally, all GNU/Linux systems are free – they're all cost-free. What you pay for is consultancy and support in the pro versions. GPL licenses are genuinely respected there :)