Today I received my Google Project Fi package including a micro SIM card.
The Project Fi SIM card needs to be activated in an Android phone via the Project Fi App.
Once the SIM card has been activated, you can put it in your iPhone 6s and you should get signal immediately.
Note: You might need to restart your iPhone after the SIM has been inserted to pull the settings from the Project Fi carrier.
Even though you have signal now and you might see 4G on the top, you will notice that the internet isn’t working on your phone.
Step-by-Step Instruction To Setup Project Fi Cellular Data
Go to the Cellular Data settings on your iPhone 6s and you should see only the Cellular DATA APN settings configured, as shown below:
In order to use the internet via Project Fi on your iPhone 6s, change the Cellular DATA APN from alpha to h2g2.
Note: If cellular data doesn’t start working right away, change into Flight mode and back. This will re-apply your cellular data settings.
Following the steps above, got my iPhone registered with Project Fi and allowed me to start using cellular data successfully.