What that is is a PC Card that can read SD, CF, and other memory cards (like those used in most digital cameras). It is just a little unique in that it is both a PC Card (PCMCIA) and a USB device.
Put another way, it is a PC Card just like your AT&T Edge Card, not a PC Card host that you can put the Edge card in.
I don't think you will find a USB adapter that is a true PCMCIA host. I found a couple of card readers by googling for "usb to pcmcia" but no hosts. The distinction between a reader and a host is a reader can get stuff from storage devices (like pcmcia drives) but not run something like your edge card.
Ok, I found a host (it was about the 5-10 links down on the "usb to pcmcia" google).
http://www.arstech.com/usbpcmcia.htm I know nothing about the product or how difficult it would be to get, but this is the
type of adapter I believe you are looking for. Hopefully that will help narrow the kind if thing you need.
EDIT: Thought I would clarify. Arstech appears to be an industrial solution not a consumer one (i.e. they do not sell to end users but to companies like Belkin who then package and sell the product) So you probably won't be able to get one of those. It is just the only example I could find of what I think you need without spending an undue amount of time searching.