I'd like to port my phone numbers from google, as I'm afraid the migration of the free domain may cost me my phone number in case of shenanigans (like google voice being considered separate of google mail etc)
If you're actively managing a large number of users and devices, I had great luck with OnSIP. They're not the cheapest game in town, but their management interface is top notch. They were always innovating and the architecture they disclosed was impressive; very focused on HA and performance.
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.
CUCM: https://twilio-cms-prod.s3.amazonaws.com/documents/InteropGu...
ISR: https://www.twilio.com/docs/sip-trunking/sample-configuratio...
They also have a porting process you can use to migrate your numbers from GV/Bandwidth (or you can just buy a Twilio number for $1).