Google being Google completely fucked up the UX on inbound call routing. Lets say you enabled data calling to try it out because why not, they actually put something in the changelog other than 'bugs and fixes'. This will immediately break inbound calling and de-select routing calls to your phone numbers over carrier. Then if you reverted the setting to carrier, it just make it so calls went nowhere.
I've had a Google Voice number as my primary for over a decade, it took me a few days to notice none of my calls were ringing inbound. It took me over a day to figure out how to re-enable it, because you couldn't just have the line paired, you had to enable inbound calling in the app to both the phone and the app.
Google still maintains two different panels for Google Voice. This has been the case for a couple years now. Both have different features, anything important like porting and setting up voicemail manually will have to happen through 'legacy Google Voice'. It's insane.
(Obviously iMessage is different because it's not actually MMS)
Google Voice is actually a safer bet as there's no doubt all sorts of legal snares they'd hit if they shut it down. Bandwidth.com runs things behind the scenes and is a competent company to do business with. They'd likely have to spin it off if they wanted to discontinue it.
I give out my GV# (I use call-screening) to everyone (esp. businesses) and put it on my gmail .sig.
I get almost no spam calls at all.
It sure looks like they do. Spammers have been calling our office lines daily (including numbers that aren't assigned to anyone and aren't given out). The spam calls come in numerical sequence. They're clearly just working through every possible phone number, in sequence.
Eventually after I realized it was silently dropping group messages because they were MMS and Google never worked on supporting MMS (images were dropped too back then) I left it for iOS and iMessage. Getting dropped from group chats meant people thought you were ignoring them and you'd miss invitations.
Google had a huge lead with voice that they wasted instead on Buzz, Allo, Talk, Hangouts which all were killed or are being killed - I wouldn't go back.