Just tested out decoupling my Google Voice number from Hangouts thanks to the new Voice update. Mixed results as of now. After decoupling:
• SMSs are sent and received only through the Google Voice app and voice.google.com, no longer in the Hangouts app.
• The Google Voice app and website don't support making or receiving voice calls at all.
• When I call from the Hangouts app, it still shows my Google Voice number as the caller ID.
• Receiving calls to my number rings through Hangouts *only* on my phone. (It used to also ring through Gmail on my computer.)
Tested using the Google Voice iOS app. Thanks to @eayoungs for helping me test this out!
The Google Voice iPhone app found a very clever way to make calls.
When calling someone, it used to first call you, you'd answer and then it would ring the other person.
Now it seems to make a request to the GV servers and dynamically allocate a phone number to your target, then it tells your iPhone to dial the temporary number which they forward on to your target's phone number.
The end result is seamless! Go to the GV app and dial a number, and it Just Works™