Although advertised as unlimited, this new plan comes with 22 GB of 3 Mbps data, but the video streaming speed is limited even more - just 1.5 Mbps from the start, and all for a monthly fee of $60 USD . In these conditions, 720p or full HD video streaming are both impossible.
http://www.notebookcheck.net/AT-T-unveils-GoPhone-unlimited-data-plan.206702.0.html