The latest iteration of Google Voice has chat, for example, while SMS support inside the Hangouts Android App was removed on purpose and users told to use yet another app, first called Messenger, now called Messages.
All their communication products suffer from convergent evolution, yet remain in dizzyingly varying states of integration with each other.
[1] https://blog.google/products/google-voice/ringing-2017-updat... [2] https://news.ycombinator.com/item?id=13463940
I use google voice and hangouts. I can both send and receive voice calls using my google voice number via hangouts. I can also send and receive sms message using my google voice number via hangouts. Both of these have been true for at least 4 years, maybe 5. They started trying to phase sms out of hangouts a few years back, but never removed it for google voice users.
They could have a seamless bridge between them, though. They sort of tried: you can dial a phone from Hangouts, but not back, or you can receive your Voice text messages in the email, but not send a reply back (afaict).
Google is notoriously bad at cohesive product management. They have a number of bright ideas, but no visionary in the consumer product space, so apparently no coordination.