The information below was posted on a FatWallet forum that Google has an approved 3rd party API for using the Google Hangouts Telephone service by providers such as Obihai:
News from 5-17: Google Forum.
Google Hangouts has a new Telephone API for 3rd Party support:
« on: May 17, 2014, 06:18:59 pm »
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Appears to be new 3rd Party Support for Apps and Devices.
https://developers.google.com/+/hangouts/telephone-oauthContact Obihai, GrooveIP, Talkatone and such & let them know. Wink
This is official 3rd Party support from Google. The previous way was a hack that was not okay by Google. Keep that in mind.
I don't think Obihai is aware of this official API by Google. No 3rd party is yet. It just popped up out of the blue. I'm sure Google will make an announcement eventually.
Link Above:
Telephone APIs: OAuth requirements
The telephone and billing APIs provide access to the user's Google Voice balance and allow applications to place calls on the user's behalf, possibly costing them money. As a result some methods will only work if the user has granted access via an OAuth scope that the user must agree to when starting the application. Here are the steps to add the scope to your application:
Open the Google Developers Console.
Choose the project that contains your Hangout app.
Choose APIs & auth, find Google+ Hangouts API, then click on the gear icon () to the right of that service name. to get to the settings screen.
Check This application requires additional OAuth 2.0 scopes. This opens a field.
Copy and paste this scope into the field:
https://www.googleapis.com/auth/hangout.telephone.Click Save.