Don't do it! No matter what, don't jump to a carrier offering tiered data! No matter how much you want the phone! With the data usage that 4G LTE would make convenient, your bill would increase by 100 easily. Less if you don't do any streaming of videos or music or files from the cloud, but then what would be the point of getting a new phone?
If we speak with our dollars, maybe they'll listen. AT&T, when frustrated that it's difficult to increase their user base, may conclude that raising the price of unlimited by $10 to $20 would garner more new customers than the inexcusably lousy tiered price model does. This would hopefully force others to follow suit. We need to make them know that the tiered model does not work for us, even if it means we don't use data or have these nifty and expensive smart phones.