Nope, a "Transfer of Billing Responsibility" with AT&T will NOT transfer unlumited data. I learned this the hard way a few months ago when I took over a line from someone in the XDA Marketplace. AT&T told me to wait a week and call them back but the request was denied like the person above me. That was probably just to stall for time and get me off their backs, though...I didn't want to make the person who gave me to line to take the ETF so I ended up paying it.