I can answer that.

It started last spring, with the leak of an AT&T Mobility internal memo asking store staffers not to schedule vacations between mid-June and mid-July — four weeks that neatly bracketed what turned out to be the June 29, 2007 launch of the original iPhone.

The same thing happened again last month; this year, AT&T (T) employees have been asked to stick around for the four weeks starting June 15 and ending July 12 — roughly corresponding to the expected launch date of iPhone 2.0. See here.

So what are we to make of the report from AppleInsider that Apple (AAPL) retail staffers in some regions have been informed that back-to-back vacation days during that period are forbidden, as are multiple weekend absences, from the third week of July to the second week of August?

According to AppleInsider, the vacation blackout has to do with a bigger-than-ever back-to-school promotion, the details of which are expected to be revealed to Apple’s higher-ed partners Monday at 2:30 p.m. ET (11:30 a.m. PT).

And what about vacations in June, when the 3G iPhone is supposed to arrive? Perhaps Apple Store employees don’t need to be told that if they aren’t on hand for the first big weekend, they needn’t bother coming in Monday.

[Update: Reader T-Shirt from Richardson, Texas, in the suburbs of Dallas (where there are three Apple Stores) has it on “very good” authority that Apple retail employees have the same vacation black-out dates as do the AT&T wireless employees.]

[Update 2: I kicked this around a bit more and as near as I can tell, there doesn’t seem to be anything to either of these rumors. Go ahead and take that vacation, Mr. T-Shirt.]