I've seen the commercials. I'm sure you have too! AT&T Wireless touting their unlimited data plan. Now some customers are complaining about a new policy that seems to punish those who use it most.

It's data speed slowdown that becomes the issue for a group considered in the top 3-5% of users. A slowdown of almost 99% in some cases. making the download extraordinarily long. If you are a heavy user of AT&T's data, be aware.