Ever since the announcement of Project Fi, there has been a lot of buzz around the service and the notion of being able to switch back and forth between Sprint and T-Mobile networks when WiFi wasn't available to handle the service. Project Fi also gained a lot of attention for various other reasons, including its limited compatibility to one device, the Nexus 6, and for the fact that Google would not only let you pay by the GB for data based on how much you personally think you need from month to month, but refund you money if you accidentally ended up buying too much.
Yes, for all intents and purposes Project Fi is shaping up to be a decent option for wireless service for some individuals, although this hinges largely on how much data they use on average and whether or not the same amount of data on Project Fi costs less than, or is at least equal to their existing wireless carrier package. Another major point of concern or interest has been the compatibility of Google Voice, or more specifically how activating a Project Fi number would affect the use of Google Voice on one's Google account. That's assuming you have a Google Voice number activated in the first place, as many don't. For those that do however, and use it consistently and often, this has been a burning question. Would Project Fi and Google Voice work together harmoniously on one device? The short answer is no.
Over at the Project Fi support page, Google has listed a help category as "switching from Google Voice to Project Fi." If the name of this help category doesn't sum it up, Project Fi essentially replaces Google Voice for you if you activate a Project Fi number. In completing a Project Fi setup, it doesn't just discontinue Google Voice from the Nexus 6 you're using Google's new wireless service from, it discontinues Google Voice from your Google account altogether. While this may not sit well with some users, Google does mention that Project Fi can handle many of the same things Google Voice has been providing for a while, using voicemail transcriptions and call forwarding as an example. They also explain in detail what gets moved over from your Google Voice number when you set up Project Fi, which includes your voicemail greeting, your voicemails, your call history, and your texts all sent from your Google Voice number so there is no worry about losing those particular things.
Google lays out a few other steps in the whole swapping process, and if you're planning on moving your Google Voice number over to Project Fi, it is possible to do by simply choosing one of the designated options when you sign up for Fi, however the transfer doesn't actually start until you have your Project Fi phone, which in this case, is only the Nexus 6 at this point in time. As for what isn't available with Project Fi that you did or do get with Google Voice, if you happen to make the switch you'll lose things like spam filtering, call recording, call switch, conference calling on the fly, incoming caller ID, and outgoing caller ID. The switch also disables access to Google Voice apps from the web. Lastly, if you have credits with Google Voice that you've already paid for, you can either request a refund before the transfer to Fi, or you can leave the credits be and they'll be moved over to Project Fi when you switch, presumably transitioned into money towards your monthly bill. If you need more information, you can find all the details about switching from Google Voice to Project Fi via the help page listed below.