"This device might be restricted to the original carrier"

See this Apple support article—>How to unlock your iPhone for use with a different carrier - Apple Support

Why can’t you ask them? They are the MVNO the phone is locked to.

A flex policy phone automatically locks to the first carrier it is used with; the carrier doesn’t have to take any action. In the unlikely event that it is locked to t-mobile they have a very liberal unlocking policy.

Well that answer that question. After contacting Google, they emphatically said they 'do not lock devices, best buy did that, contact them." Word to anyone who is reading this. Never, ever connect your iphone to Google Fi.

This is not a good answer. I bought an unlocked iphone from Best Buy 2 years ago. I've been using it on Google Fi. Google Fi has limited iPhone support, but they do not lock devices. Some over that period, the device is now locked, but to who? I don't know who. It doesn't say, it has never been on another network. Now I am trying to change to another provider, and the phone is locked. With no carrier to unlock it.

I am going to give it a try, but from what I am seeing in discussions is they don't lock phones. But they will use the T-Mobile network, potentially the phone might be locked to that. If that is the case, I have no account with T-Mobile, nor have I ever had an account with them.

Can't ask them about it. Google Fi doesn't lock phones. 100% sure they will say that, or that they use T-Mobile for all iPhone communication. But I don't have an account with T-Mobile, so they won't unlock it either. So if there is no way anyone can unlock this, are you telling me that my $1000 iPhone is now a brick?

Best Buy does not sell unlocked phones and never has. They sell “flex policy” phones that can be used with any US carrier, but will lock to the first carrier they are used with. So it’s the carrier you first used it with that it is locked to. Ask them about their unlocking policy.