I started the process similar to you and wanted to mail to business address. I ended up choosing residential, then put the company name in the last name field as C/O..... I am going to call VZW and tell them to fix it, but saved me the hassle of fighting there system.
I called them today as well to see if I could change the shipping address and it was a no-go. The CS Rep said that my order was still being processed and thus could not be changed. She said to call back once the order was done being processed... but that because these iphone orders are being "processed differently" there was no guarantee that changes would be able to be made.
Not a huge deal, I suppose... just a pain in the rear.