I've migrated everything from Google except for Google Voice. I have yet to find an alternative that can match the feature set and ease of use, regardless of the cost.
EDIT: asking because I've been working on an alternative of sorts. I used GV a lot before I figured I could go without it/Google.
I previously looked at jmp.chat but they didn't really inspire confidence on the security front.
I like the muti-platform integration of Voice. I use it on my iPad, on my Android phone, and mostly from my desktop. It works well on all platforms.
When I'm at home, I mainly use my VoIP phones. GV forwards to them, and they spoof my GV numbers when I make outgoing calls.
I like the spam text and call protections that GV provides. I believe they're partnered and integrated with Nomorobo.
I also have jmp.chat. It has capabilities that GV doesn't have, but it's not well integrated. (I use Cheogram on my Android phone, but there's no easily usable client on my iPad, or my desktop.)
Yeah and imo Google has better account access controls than any other mobile provider, especially if you enroll in the Advanced Protection Program.
The main downside of GV that I didn't have with jmp.chat is that numbers are almost guaranteed to be detected as VOIP which sucks but whatever.
And, possibly most importantly to me right now, my current phone has only a data connection and I make and receive calls using the Voice app. I think SIP eats too much battery and data and doesn't work well for wifi<->lte switching, but it's been a long time since I used it much.
I don't like they way they've made it harder for me to see what they actually offer vs. what I offer myself (with my FreePBX VoIP client). I wish they would (maybe on a separate page) show the capabilities of their SIP trunk. E.g. Does it support SMS? Does it support video calling? Does the client require a static IP? Etc.