Well Well, check out this little tibit from the TreoCentral Forums:

A mention today in the 750 forum makes the third instance I have heard that the ATT WM6 upgrades are being held up by the delays of GMM 5.0. Sources say that the ROM has been ready for weeks now (as witnessed by the dozens of successful upgrades with the "leaked" ATT ROM at places like XDA). However, since the GetGood functionality is part of ATT's base ROM, and since GMM 4.x versions are supposedly incompatible with WM6, the whole shooting match is waiting on GMM 5.0 to be complete.

Read: GMM 5.0 Holding Up WM6 Upgrades for ATT Devices - TreoCentral.com

Nice sleuthing there, WDW. Good Messaging, if you didn't know, is a great little push email alternative to Exchange and Blackberry for Windows Mobile (and PalmOS), which was acquired by Motorola. This whole theory should be taken with a grain of salt, though, as GoodGuy mentions that it gives "Good way too much credit for holding WM6 up." I'd tend to agree with GoodGuy, but something's holding things up, and I'm losing faith in my belief that it's because AT&T wants to drop WM6 for the Blackjack, 8525, and Treo 750 all at the same time. The ROM's for all three devices are, I believe, ready.