The Guild Wars 2 Extended Experience free mobile app for playing GW2 on your smart phone, will release to mobile and browsers soon. ArenaNet will be connecting the app to the game servers, allowing players to check on some social items like guild news, vaults, the auction house, etc.
Players can use the app, even if they aren’t connected to the game on their PC, to auction (buy/sell) items in the game, organize vaults, and talk socially with guild mates and friends.
While hardware limitations keep the app from allowing actual game play, it can ping specific map points on the GW2 world map, check player stats, etc.
The app still has not released, but early beta versions are being show, so release is likely imminent. It will be free to GW2 players.