One of the big misconceptions about Project Fi is that you are absolutely required to use Google Hangouts for your SMS/MMS and Instant Messaging app. Here is a quote from a post I made a couple of weeks ago on the subject: If you are a new Project Fi users, chances are you are a bit confused. That confusion surrounds SMS and which app you can use for getting your text messages on your Nexus phone using Fi. On the surface, it looks like you are required to use Google Hangouts, the voice, video and yes, text messaging integrated app. But that not necessarily true and in fact, even Google suggests that you use Google Messenger, the default SMS app on Nexus devices, for texting.
That said, for those of us on Project Fi, there are some benefits to having everything in one app like Hangouts. Not only does it give you one app to go to for your communications, the information synchronizes with Hangouts on your PC. That means you can get your messages and your texts on your desktop, read them and reply to them. If you haven’t considered moving your SMS/MMS communication to Hangouts, read this article and see if it is right for you. A lot of it will depend on how you communicate and with whom. But after being an avid Messenger user for most of 2015, when I switched to Project Fi, I embraced Hangouts and haven’t looked back.