I'm a Fi customer with an iPhone, and when April of this year rolled around, I was living juuuust outside of cell service, thus relying heavily on Hangouts to forward SMS and provide voice calls.
Google was supposed to replace this with something called, I believe, Messages by Google. But somehow they didn't manage to release this for iPhone... like ever as far as I can tell? Or at least not so far.
So I was stranded without the ability to make voice calls for two months. Paying customer mind you.
To be fair, Fi was an amazing deal when I was doing a lot of international travel, and I've stuck with it because the pay-as-you go aspect is still pretty nice (and because international travel will presumably return someday).
But part of me wishes that after Reader was canceled I had just pronounced anathema on the whole company.