iPhone Tmobile unlimited plan

Has anyone used their iPhone 4 on T-Mobile? I know the data speeds are Edge but there is this new plan coming out and I wonder if it is worth it. http://www.bgr.com/2011/10/03/walmart-and-t-mobile-to-launch-30-prepaid-unlimite d-plan-on-october-16th/ I would prefer to stay on ATT and get a data only plan like an iPad plan for my iPhone, but I don't think they do that. I am out of contract this month and sick of paying out the butt for minutes i don't use. I'd like to just text and use data, and call for emergencies only.