Sony Ericsson Z550a

I'm considering buying this phone as I had good luck with a Sony Ericsson Z520a. Looking on EBay, there are no Z550a's currently for sale, but Z550i's. I assume this is an international version, it seems to have the same specs, but I'm wondering if this will work with AT&T (Cingular). It's unlocked, and AT&T says they will provide me with a sim chip at no cost. Also, are there any other differences between the Z550i and Z550a?

Why is this phone not available in the USA?

doesn't carry Sony Ericsson's phones. Why is that?

z530 replacement, yet no EDGE support?

Megapixel camera, yet no expandable memory?

I can't see us (at&t) picking this phone up. Customers are reluctant enough to try Sony Ericsson and this one doesn't exactly make a stranger feel warm and cuddly.

...but handsome.

Better than your average Samsumg flip.