I believe the ios (iphones) is still in beta testing? Yes?
DH has had google fi account forever. Mostly uses it as a secondary line for travel. I use one of his four data only sims in my iPad so I think it works on IOS. I use my google voice account and make and receive calls to the iPad and forwarding my home phone works in places like Scotland England Canada peru and New Zealand. Never got a voice phone sim like DH has though.
Oh and I did use the data sim in my iPhone se6 last trip and it worked fine. There are still limited phones for use under android too.
We bought a Nexus 5x from google when we signed up for the google fi service. At the time it was the cheapest option. It is our only android. The camera on the Nexus 5x phone is pretty nice for the price.