Bandwidth.com mostly runs that service and they have proven themselves a competant business that Google built other products like GOOG-411 off of. Google Voice is just a frontend to it.
I think if it ran entirely on Google's infra and the service itself could be killed like the registrar was it would have been killed years ago (notably it stagnated from like 2012-2018 or so and there was a period of time they had a half-assed panel redesign and the product blog for it wasn't updated for years)
You can but they don't really do B2C, their B2B has come down for small businesses but still requires a larger commitment then makes sense for a phone number or two.
Unrelated, but I've found it bizarre Google Voice doesn't do RCS but they made a big push otherwise to enable it for their Messages app.
I think if it ran entirely on Google's infra and the service itself could be killed like the registrar was it would have been killed years ago (notably it stagnated from like 2012-2018 or so and there was a period of time they had a half-assed panel redesign and the product blog for it wasn't updated for years)