Store 1: "We're supposed to have them in a couple of weeks."
Store 2: "We'll have them on May 6."
Store 3: "We have them in stock. Oh, hold on a minute. (long pause) I'm sorry, we're not allowed to sell them until the 10th."
Store 4: "Yes, we have them in stock."
In other words, there was no shortage of variety in sales reps' stories. I don't know how this happens -- it's conceivable that AT&T really is telling each store something entirely different, but it seems far more likely that these guys simply haven't been effectively educated on what's going on here. At any rate, I was able to march down to the fourth store I called and pick up the MicroCell with no hassles, therefore ending a many month-long personal nightmare of mine (and by the way, the device works just wonderfully).
The lesson learned? Even if the MicroCell hasn't launched in your market -- that is, you go to AT&T's MicroCell site and it tells you it's not yet available in your zip code -- be persistent and keep calling around. You've just got to find that one sales guy who's willing to flip it.