ATT Dsl 
   The att dsl product is much like your high speed cable service. Other than being significantly cheaper, and more choices on the level of speed you want.
A major difference between att dsl and cable is with dsl you're not sharing your bandwidth with other customers.
   Your att dsl signal is dedicated to you. This happens because it rides your phone lines from your house to att's equipment. Therefore it never gets combined with other customers. With a cable system once the signal leaves your house it's combined with everyone else's in your area and this can cause a pipeline slowdown.
This can cause a major decrease on the speed of your internet. Here's a funny commercial showing the results of bottle necked traffic on a cable system.