Project Fi is Now Google Fi and reaches in to iPhones.

Snapvoip

After 3 years since the start of the Project FI, Google is setting it's mark in the Mobile arena with the newly named Google FI.
Even though one could get a data-only SIM for iPads as secondary devices before. A Fi SIM has always worked in an iPhone too but one had to adjust the data settings on the phone.
Now Google is supporting  new iPhone customers directly, through a beta program and requires “a few extra steps to get set up.” There is also this Google Fi iOS app to help the process along.

Google Fi is a “mobile virtual network operator.” or MVNO, which means that your actual service comes from a few carriers; Fi uses T-Mobile, Sprint, and US Cellular as its backbone. However one needs a phone like the Pixels and others that Google sells) are capable of dynamically switching between these networks. Like before, phones that aren’t explicitly “designed for Fi” are stuck on T-Mobile’s network. So any iPhone user will be stuck in the T-Mobile. Project FI