Route all international calls via Google Voice when dialed from iPhone phone app

In android phone, I can dial an international number from contact or phone app, international calls would be placed from Google Voice instead of using Carrier. And, it prompts that I dialed an international call and tells me that price of the call. How I can do the same in iPhone? is it iPhone issue or Google Voice issue? I see its more of iPhone issue it won't allow other phone apps to take control of iphone phone calls.

I understand that I can open Google Voice app and place an international call. The above was just convenient. I can dial both domestic and international call right from phone app, domestic calls routed by carrier and international calls routed by google voice.