Most ISP's, and that includes Comcast, ATT, and Verizon have data use caps per month. Unlimited Access is differet from the old unlimited bandwith.

Comcast has raised the cap, they also plan to raise it again for 2013, and not count streaming services linked to them (infinity watching) with the new higher speed systems (the 50mb, 100mb, 300mb, 50mmb down, 50, 100, 200 up services). Business lines have no cap.

ATT began throttling connections again, never liked them anyway. IT depends on what you signed up with. THey also have a cap.

Verizon, has a cap, but it's on 1 direction.

Caps, as far as with Comcast, are recommended usage caps. If you go over once, they let you know. If you go over to much again, they send a warning, if you go over yet again, repeatable taking advantage, then they can cancel your account. You realllly have to be pushing it to go over the new cap.