I have an iPhone X and it works perfectly fine. By them not yet *fully supporting", it means you have to get your voicemails from the Google Fi phone app instead of from the voicemail feature. But it does email transcription and text transcription. (of the voicemails)
At any rate, I gotta imagine it will improve as time goes on. The service is relatively new.
And echo Mike... it should be much cheaper than Verizon, depending on use. It is definitely much cheaper for my use - heh. Verizon internationally is very expensive. I use the $20 plan because I am usually on WiFi and I have a primary sim that provides me unlimited data... so basically I get phone and text on a US number for 20 bucks per month internationally.
Interestingly enough, you can only activate google fi from within the continental US (and maybe Canada and Mexico), and they detect all the common VPN services. (I tried several.) I built my own openvpn server at aws and was able to activate my phone by connecting to my computer wifi sharing which was connected to the openvpn server in Ohio. It is a bit of a cheat, but I was no longer in the US when I found out about this service. Otherwise I would have had to wait until I was back in the US for a company event to activate the phone - heh.