I hate to be that guy, but if you don't mind being a Linux sysadmin you might consider running your own Asterisk server. I do that for my SMB with about a dozen

I hate to be that guy, but if you don't mind being a Linux sysadmin you might consider running your own Asterisk server. I do that for my SMB with about a dozen physical sets, and use Twilio for SIP trunking. I followed the first 10 chapters or so of the O'Reilly Asterisk book making a few changes here and there to suit my preferences (different Linux flavor, different DB). I run a $10/month Digital Ocean droplet that hosts the Asterisk server. If you can deal with config files, you can have a rock-solid PBX with Enterprise-grade features for the cost of the server + Twilio's SIP trunking features. It ends up costing about $25 every 1.5 months or so. I barely ever think about it, except when I need to tweak a greeting for holiday hours or something.