Project Fi is a test from Google of a new way of delivering mobile phone service.
I signed up for the service and got my very nice box of free goodies in the mail about a week ago. The package includes an external battery for recharging a phone or other device, a nice set of earbuds with an extra jack for a friend to plug in and a bumper case for the Nexus 6, the only phone that currently works with this service.
Project Fi uses both Sprint and T-Mobile in the U.S., plus open wifi networks, seamlessly switching between them. It also features a data plan that works like a budget. You set a limit but if you go over, there aren't penalty charges. You always pay the same amount per unit of bandwidth. Internationally, it is supposed to offer good rates and free texting.
When I signed up I gave Project Fi my Google Voice number but had forgotten that long ago I'd switched that number over to my own corporate account. Project Fi only works with @gmail accounts not corporate accounts. It took a little while for the excellent customer service folks at Project Fi to figure out how to handle the situation but in the end it made sense to take a new number for my @gmail account. This left me with my old number, the main number I use on business cards etc, still associated with my corporate account and still associated with Google Voice but not associated with my new Nexus 6. However, this isn't a problem as far as I can tell. Here's why: I can use Google Hangouts to receive and send texts from my Google Voice number as well as my new number which no one knows. And I can use the Android Hangouts Dialer to make calls from my Google Voice number. I think this is a fully workable situation. So, I'm therefore able to use two separate numbers on my new Project Fi account on my Nexus 6 phone--my corporate Google Voice number that everyone recognizes plus my new, unknown Project Fi number that's the number associated with my Nexus 6.