Google has just launched its own wireless cellular service, called Project Fi, which operates on top of Sprint and T-mobile's networks. Google calls Project Fi "a program to deliver a fast, easy wireless experience in close partnership with leading carriers, hardware makers, and our users." The service integrates with Google Hangouts, so you can place calls from your number on any other device with Hangouts enabled. So far it's invite only and just for Nexus 6 users, so the roll-out may be a bit slow to start. Still, wifi tethering is included and with no contract, it may be a popular option. You can request an invite on their site if you want to see if it'll work for you!