It starts in about a week, and the required Nexus 6 phone is on sale until Friday at Amazon for “only” $350. It does not sound like any other phone option is likely in the near future. $10/month for unlimited calling & texting, and $10/GB for data, with any unused data credited back the following month. 120 countries are included in that unlimited texting and data, BTW, which makes this a great option for travelers.
I’m surprised there doesn’t seem to be any mention of it here yet.