Went to sign up for SkyMiles via AT&T Wireless and found that the offer doubled + ongoing earn:
10,000 Delta SkyMiles for activation on plans $59.99 and up with a two year agreement,PLUS earn 1 mile for every dollar spent on qualifying wireless usage each month!
Can still get 5K for plans below $59.99, but you don't get the ongoing earn as well.
http://www.attwireless.com/yourmiles/att_delta.html