Google Fi only allows Their Nexus and Pixel phones on their network. It is like an ISP seeing that you are running Linux and not letting your traffic through, just a bit more complicated than that. (SIM Card, Modems, Frequencies)

This sounds a bit misguided. IIUC, Google Fi is really a mechanism of accessing two carriers from the same device. It consists of 1. A partnership between Google Fi (the cellular provider), T Mobile, and Sprint, and 2. A special radio hardware on the phone that is capable of working with two different "channels" at the same time. Since my Nexus device broke, I have personally been using "Google Fi" (the provider) on my iPhone which means I do NOT reap the full benefits of Fi without having the special radio hardware.

So, I don't think it is physically possible to do the "two provider at the same time" thingy without a special hardware (you'd need two parallel "radio" circuits on your phone).

And with that, your analogy falls sadly on its face, as you seem to indicate an artificial "software" limitation has been set to prevent us from using Google Fi on our iPhones.

Sorry, I did not mean to say that is how it is but how it seemed. My understanding is that the modems aren’t capable. That being said, activation is done only with a nexus or pixel device (software) and while switching might be a hardware issue, iPhone works on both sprint and Tmobile (on an iPhone on Tmobile after moving from Verizon) and so google fi should still work.

As I mentioned, I AM already using Google Fi on my iPhone. What does not work is the hardware feature of handing off between providers mid-flight. With my [now deceased] Nexus X, a call would seamlessly [to me, anyways] switch between providers during medium/longer commutes. With my iPhone using just T Mobile, calls get dropped during my daily route as there are certain "T Mobile blind spots".

Sorry, I completely misunderstood. Thanks for clarifying!

Is it actually a special radio, or just features which normally get disabled by e.g. Verizon programming the baseband? I'm assuming that the "special" radios are simply NOT using crippleware and setting some other registers which could be enabled on many more devices...if carriers played ball, which they don't want to for obvious reasons.

I have to research deeper to be sure (there is some FAQ at https://fi.google.com/about/faq/#supported-devices-7). But skimming through that page, I suspect this is a new-ish feature not available on most smartphone radios.

You can pop a tmobile SIM in the phone and they partially work, but Google Fi requires hardware support in the radio to work fully

It's not that they're blocking iOS, but more that iPhones don't support the network.

Understood. Just wish they would both get on board with it.

Not quite. You need those phones to activate service but you can move that sim into other phones later. Once you have service you can also get data-only sims that openly support all devices.

Can you still recieve sms and normal phone calls? Because last time I tried, it didn’t work.

yes

Project Fi does some things to switch between several carriers (T-Mobile, US Cellular, others) behind the scenes that doesn't work as well on iOS. Also, you need a Pixel or Nexus device to activate initially anyways.

In this case, Fi relies on software in order to switch between different carriers and wifi.

They are not able to implement it to their satisfaction with iOS, so they stick with their own devices.