Hello All, does the charge for wireless or Shipping need to be done on the main card or can it also be done on an AU's card? There is an AT&T Amex Offer on my Biz Plat AU card (NOT on my main Amex Plat card) and I want to double dip - so checking if the 20 dollar statement credit will be applied if the charge is made on the card's AU card? TIA!