Project Fi by Google
For those who don't want to read the FAQ or find the video incredibly unhelpful [1]:a. It only supports the Nexus 6 out of the gate.b. It automatically switches you to the "fastest" network available. Partners out of the gate are Sprint and T-mobile. Sounds like it prefers Wifi, then 4G LTE, and then degrades down to 3G or 2G.c. Pricing is $20 for unlimited talk (domestic) and text (domestic and international) and wi-fi tethering. Data is $10 per Gig. (Plus taxes, etc.) No support for unlimited data. they also refund you all the unlimited data at the end of the month.d. No annual contract required.e. Supports calls over wi-fi.Coverage map here: https://fi.google.com/coverage[1] Not even sure why they made a video, it doesn't explain a thing...Edit: clarified domestic talk pricing, and refunding data.