While the app is free, you do need to be a subscriber to one of a select few cable companies and have a plan that includes ESPN. Up until today, the group of cable providers allowing you to access WatchESPN did not include Comcast. But now, subscribers to that provider will be able to authenticate their service and receive the streaming video as well. The ESPNNetworks enabled providers are Bright House Networks, Comcast, Time Warner Cable & Verizon FiOS TV and if your service includes ESPN, you can watch all of the different ESPN channels on your mobile device. If you don't receive television service from any of those names, but do get high-speed internet from Verizon, you will have access to ESPN3.
The only downside to having ESPN wherever you go is the hit to your monthly data cap, and the hit from your girlfriend or wife who will have to schedule an appointment to have a conversation with you.
source: WatchESPN via Phandroid