I didn't realize the infrastructure differences were so significant:
http://www.bgr.com/2012/08/31/lte-iphone-hurts-att-helps-verizon/
Also, as is you needed more evidence, if you missed this fun little nugget last week from these jokers:
http://arstechnica.com/apple/2012/08/att-wont-charge-for-facetime-over-3g-but-will-require-shared-data/
http://techcrunch.com/2012/08/22/att-defends-facetime-over-3g-decision-says-it-isnt-violating-net-neutrality/
http://www.theverge.com/2012/8/22/3260024/at-t-responds-predictably-to-facetime-controversy-says-claims-of-fcc
http://www.bgr.com/2012/08/31/lte-iphone-hurts-att-helps-verizon/
Also, as is you needed more evidence, if you missed this fun little nugget last week from these jokers:
http://arstechnica.com/apple/2012/08/att-wont-charge-for-facetime-over-3g-but-will-require-shared-data/
http://techcrunch.com/2012/08/22/att-defends-facetime-over-3g-decision-says-it-isnt-violating-net-neutrality/
http://www.theverge.com/2012/8/22/3260024/at-t-responds-predictably-to-facetime-controversy-says-claims-of-fcc