If you use the Cheogram app for JMP.chat it works like a normal call and messaging service. You can make phone calls through the dialer app or cheogram and send and receive messages through cheogram. The app takes you through setting everything up on the first run. The only issue I've had is that group messages only show the phone number and not the contact.

That being said, if you're only using it occasionally, Mysudo has a $0.99 plan while JMP.chat is $4.99.

VoIP.ms?

It's what I use. I'm not sure of making phone calls, though.

You could check this out, but it looks like it might only be USA and Canada:

https://mysudo.com/mysudo-plans/

I think Asterisk can do all the functions of Google Voice. I looked into self-hosting Asterisk, but I think it's beyond my skillset. I think there are services that host Asterisk for you.

JMP

I'd love to know how it works out for you. There's no cell signal where I live, so calling & messaging is all over internet, anyway.

Cloaked or mysudo