Best VoIP usable on Desktop

Can you suggest a VoIP that has the following characteristics?

\- Can be used on desktop as well as mobile
\- Allows for the use of multiple phone numbers (different numbers for different purposes)
\- Privacy oriented

After listening to a few privacy talks I am looking to move my phone use to VoIP. I am on my desktop for much of the day and a number of options mentioned don't seem to have desktop apps.

Any suggestions?

Thanks for …

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