AT&T is conducting an experiment with Wi-Fi at the Dallas-Fort Worth International Airport that could lead to much more ubiquitous free Wi-Fi. The project, which GigaOM understands is due to start in September, will let anyone get on to the carrier's Wi-Fi for free if they watch a 30-second ad once every 40 minutes. Normal access for those who aren't already subscribers to a qualifying AT&T service either costs $4 per use or $20 per month.
