If you want an open source walkie talkie functionality, you can use signal, or even simple x, and send voice messages. Boom walkie-talkie
There are products built on top of Mumble, which is a voice conferencing software, which is open source.
https://github.com/Theofilos-Chamalis/EVO-PTT
The client is open, but they use a proprietary server, which is just mumble
If you want to host your own Mumble server, you can use a more open client that's not tied to a commercial server... Like https://mumla-app.gitlab.io/
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Being hostile towards people giving you good advice, is not a great way to get good advice in the future. The reason people are telling you about the benefits of open source software, it's impossible to vet or prove any privacy claims with closed source software. They could be lying, people lie all the time.