At T-Mobile, get two lines with unlimited data for $100 per month when you pay via AutoPay, as part of its T-Mobile One Plan. This plan includes HD video streaming and 10GB of mobile hotspot data for every customer, every month. (Those used to be add-ons for which you'd have to pay $25 per month.) Also, you'll get a bill credit of up to $10 every month for each T-Mobile ONE line that uses less than 2GB.