Does anyone know how A T & T calculates which tax rate to use on the plan when you purchase an iPhone? I live in a 'high tax' state (IL - where the effective cell phone tax rate is over 20%. See http://www.taxfoundation.org/blog/show/435.html) and would be interested in purchasing an iPhone if I could some how get the rate for Nevada. Has anyone tried to do this? Do they use your billing address? Credit card address? The location the cell phone is used most?