I finally got through and added my iPhone to the cart successfully. I then hit Continue shopping to attempt to "add a new line" and add a second iPhone to my cart for my fiance who I'm bringing over from Verizon. After hitting "Add a new line to my existing account." it loads a screen with: Visit the Apple Retail Store to add a line. If you’d like to add an additional line to your account, please visit your nearest Apple Retail Store where you can complete your pre-authorization. What? Why?