Karma was always intriguing, at least in theory. You get a relatively cheap mobile hotspot and data, but it’s open to anybody. If somebody near you uses it, you’ll get free data added to your plan. But the best part of the Karma system isn’t the scheme to try to get free data, it’s the way you pay for it: flat-rate data without any monthly plan. You pay for what you use and nothing more. If you leave it in a drawer for six months, it doesn’t cost you a penny.