AT&T has decided to stop the use of a set of very blatantly privacy-violating cookies that is capable of following mobile users on its network when they go from one site to another by inserting a series of codes. It's uncertain why AT&T decided not to go down this route but competitor Verizon Wireless continues to practice to track as many of its subscribers as possible.
But it's not quite over if you're an AT&T customer. See, Ma-Bell Wireless still reserves the right to sell information it has already collected. However, it has given users the option to opt out.
So, I reckon it's probably a good idea for you to log into your AT&T account now and do just that.
Also, if you're a Verizon Wireless customer, you can also log into your account and opt out of VZW following you.