In winter, the ski pass is your transit pass: free skibuses connect the five resort villages every 15–20 minutes during operating hours. The Flexenbahn lift between Stuben and Zürs gives an on-ski connection between the St. Anton and Lech valleys, so you can pretty much get anywhere on skis once the lifts are open.
Within each village, everything is walkable. The villages do not run any internal taxis or buses worth speaking of after the lifts close at 5pm; if you are staying in one village and want to eat in another, allow for an expensive taxi ride or use the resort shuttle if your hotel offers one.