I thought it was for a transfer wire (ex., to upload pictures or video taken with the phone to your computer or to download music from your computer to your phone). My housemate tried to buy one at the Verizon Wireless outlet, but the sales rep told her that she can't use a transfer wire because she doesn't have a memory card. Huh?? There's no memory card slot on the phone. Why would they include a Trans Flash port on a phone without a memory card slot if they only work with memory cards?

And please don't tell me Verizon's stupid, I already know that! lol

It's a slot for a particular type of memory card; see the link below.