Last week Google announced Project Fi however it only works with one phone, the Nexus 6.
Probably future Nexus phones will also support it too. It has already been rumored that Google will offer not one, but two Nexus phones this year. Huawei and LG seem to be the likely suspects. It’s also likely that Google will end up calling these devices the Nexus 5 and Nexus 6 since there is nowhere to go with the current naming scheme.
In a recent video that Google released about Project Fi, there is a device that is not the Nexus 6 but it looks a lot like an updated Nexus 5 though. However it seems that this phone just represents what is coming later this year.