This has been available on iOS for a long time, which I found to be really, really strange, given that you would think Android would be the platform where they'd want to put their more advanced features.
It isn't half bad, though -- the call quality, even when the call terminates in an actual phone number, exceeds that of cellular by a good margin, due to what I assume is a much better bitrate being used. And it works even if you don't have a Google Voice account. This is nice, because I can fire it up and make a phone call to a customer (I work for an MSP) without giving away my cell phone number. This is important to me because if all my customers had my cell number, I'd have to change it constantly or never have peace.
edit BTW, some pitfalls of this I have discovered. Depending on how well your cell handles handoffs between Wifi and LTE, your call may be dropped as you walk away from a Wifi hotspot. It works over 3G, but not well. The ringer for Hangouts on iOS is almost impossible to notice, so if you get an incoming GV call, good luck with that. I have had a good number of randomly dropped calls that I could not trace back to a cause. If you get an incoming REAL phone call on your real phone number, Hangouts (at least on iOS) immediately boots you out of your Hangouts call, even if the Hangouts call is on Wifi. (With Verizon, voice call kills LTE data stream, so this is to be expected, but with Wifi... not to be expected.)
Are we to assume that with this update, we can finally get rid of the old "Google Voice" app to do text messaging and playback voicemail?
For my use case, I ditched my iPhone 4S last year and got a Retina iPad mini with a prepaid Verizon data plan. It's pretty good, though there needs to be better integration between Hangouts and iOS. For example, if I get an incoming call notification, it sometimes will not automatically open Hangouts to receive the call. It would take me to the Home screen, then I have to open Hangouts in hopes that I can answer the call in time. If iPad's locked, then I have to act fast to enter the passcode and launch Hangouts manually.
This many not really be a problem with Hangouts than it is that iOS doesn't support deep integration with 3rd party telephony, so that the experience is no different from receiving a native phone call on an iPhone. Other small complaints are that the push notification (incoming call) sound persists for a few seconds after the call's connected, and that it only shows me the phone number of the incoming call and doesn't display the contact's name if it's in my contacts.
Considering I don't use the phone much, and have saved a lot of money by not subscribing to a smartphone plan, this overall was a good experiment. But I'll be going back to an iPhone soon because it's been a burden carrying an iPad everywhere for the past year. With Wi-fi calling now available in iOS8, I'll probably try out T-Mobile's test drive and if the coverage is good enough in my area, will probably sign up for it since they have the cheapest plans.
id much more like to have voice calls on the gvoice app... hangouts is mostly useless bloat for me. that cant even uninstall (buy a google unlocked phone to avoid carrier bloatware, only that now google is the carrier with bloatware and all)
Voice calls via hangouts has been possible on android this whole time too. Just start a video call, then turn off video and speaker. This should have been a trivial addition years ago. I can only assume it was omitted for some business reason.
It isn't half bad, though -- the call quality, even when the call terminates in an actual phone number, exceeds that of cellular by a good margin, due to what I assume is a much better bitrate being used. And it works even if you don't have a Google Voice account. This is nice, because I can fire it up and make a phone call to a customer (I work for an MSP) without giving away my cell phone number. This is important to me because if all my customers had my cell number, I'd have to change it constantly or never have peace.
edit BTW, some pitfalls of this I have discovered. Depending on how well your cell handles handoffs between Wifi and LTE, your call may be dropped as you walk away from a Wifi hotspot. It works over 3G, but not well. The ringer for Hangouts on iOS is almost impossible to notice, so if you get an incoming GV call, good luck with that. I have had a good number of randomly dropped calls that I could not trace back to a cause. If you get an incoming REAL phone call on your real phone number, Hangouts (at least on iOS) immediately boots you out of your Hangouts call, even if the Hangouts call is on Wifi. (With Verizon, voice call kills LTE data stream, so this is to be expected, but with Wifi... not to be expected.)