Looks like if you don't want to use Hangouts and want to keep using the G-Voice app you can.
However soon Hangouts will be asking you if you want to integrate G-Voice into Hangouts.
http://arstechnica.com/gadgets/2014...users-to-migrate-their-google-voice-accounts/
I'd also assume wifi/data calling with Hangouts too.
Or whenever 3rd parties use the APIs Google has: https://developers.google.com/+/hangouts/api/gapi.hangout.telephone and: https://developers.google.com/+/hangouts/telephone-oauth
However soon Hangouts will be asking you if you want to integrate G-Voice into Hangouts.
http://arstechnica.com/gadgets/2014...users-to-migrate-their-google-voice-accounts/
I'd also assume wifi/data calling with Hangouts too.
Or whenever 3rd parties use the APIs Google has: https://developers.google.com/+/hangouts/api/gapi.hangout.telephone and: https://developers.google.com/+/hangouts/telephone-oauth
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