There are several nightmare stories on the Internet regarding Google’s poor handling of payment issues related to Google Fi service. Most problems arise because people buy a phone along with Google Fi SIM. Don’t do it.

Google FI SIMs are free. Just buy a good phone without lock-in separately. The offers you see usually show up for the phones separately as well. And then order Google Fi SIMs (for free) separately. Your number porting won’t depend on whether your phone purchase went through or not. It won’t depend on whether your phone is shipped or not. If you don’t like Google Fi, you can switch back to your old carrier. If the new SIMs don’t work or you can’t pay for some reason (e.g. Google Pay frozen), you can just create a new Google account and order a different set of Google Fi SIMs for free.