AT&T, despite owning DirecTV and thus the live TV streaming service DirecTV Now, just launched another: AT&T WatchTV. Like DirecTV Now, it streams live TV to nearly every kind of mobile device and set-top box. Like DirecTV Now, it has an easy-to-navigate interface. Unlike DirecTV Now, AT&T WatchTV is the cheapest way to stream live TV. No cable subscription required, just $15 a month.