Quick facts:
$20 for unlimited talk/texts, international texts and tethering
$10 per GB (refunds $1 per 100 MB you don't use)
No additional cost for international data
Calls and data switch between T-Mobile, Sprint and Wi-Fi without interruption
Only works with Nexus 6
http://phandroid.com/2015/04/22/goog...t-fi-official/