Google Voice
The built-in iOS Contact Book allows calls to be initiated with Google Voice. So it must be possible. The GV Connect app also interacts with Google Voice app. At the simplest level, the URI “googlevoice://“ opens the Google Voice app. I really hope you might achieve Google Voice support in the near future.
Response from developer
Unfortunately this has been tested before in the past, and the results were not favourable. It didn't seem possible to open the Google Voice app from a third party app. Instead, it redirects to Google Voice's website. The googlevoice: URI can open the app but as far as I know there’s no way to pass phone numbers this way. The Contacts app can interact with other apps via Intents, which I believe third party apps cannot. Not sure how the GV Connect app interacts though. As I’m not based in the US, I rely on testers, so do let me know of any technical detail if you are aware!
Google Voice
Response from developer
Unfortunately this has been tested before in the past, and the results were not favourable. It didn't seem possible to open the Google Voice app from a third party app. Instead, it redirects to Google Voice's website.
