A leaked internal screenshot seems to show T-Mobile USA acknowledging recent reports of some G2 warranty replacements returning to customers with a tasty surprise, in the form of Android 2.3.3 Gingerbread. According to the image obtained by TmoNews, the carrier notes that this was a "test build", "shipped in error on a limited number of devices". Unsurprisingly, Tmo also says it noticed an increased number of "unnecessary" exchange requests in the week or so since the reports first emerged, as wily G2 owners attempted to take advantage of the mix-up to get an early taste of Gingerbread.
However, now that T-Mobile is aware of the error, it's unlikely any more devices will be shipped with the test build. Unless you're among the lucky few that already has it, you'll have to wait until the update's officially sent out over-the-air in the weeks ahead.