&gt; If you want something you understand and can control, you could build your own phone system with Asterisk. Inbound calls could come via VoIP (if you can find an upstream phone company you trust) or PSTN (if you&#x27;re willing to invest in having the necessary ISDN&#x2F;phone line installed, and in the hardware to connect to those).<p>If you want to install it yourself &#x2F; or not, have support, use a fully open source solution: go look at 2600Hz [0]
(disclaimer: I&#x27;m a backend engineer there)<p>[0] <a href="http:&#x2F;&#x2F;2600hz.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;2600hz.com&#x2F;</a>