I ditched my carriers about a year or so ago. Ported two numbers over to JMP.chat and all has been good. Contacts integration and using the standard Phone to make calls works well. Agreed, too, the support is great. Nice bunch of folks.
There’s a few guides or articles that might be helpful.
How to Replace Your Carrier on Android Using These Fully Open-Source Tools
Set up your Internet Phone Number (JMP.chat) with Cheogram
Dialer integration is possible using the Cheogram client but the monocles chat client is now based on Cheogram & Conversations so one could use that also. It might have a few extra options/features.
This is a nice recent write-up about JMP. Pros, cons, use cases, etc.
Going Mobile with JMP.chat | Mitch’s Blog