While the Asus mystery device has been solved, a new one featuring HTC is now afoot. Called the HTC PD29130, the phone completed testing on November 10th but just received approval this morning.
Featuring AT&T 3G bands, it is more than likely headed to that carrier though the question remains: what is it? CellFanatic thinks it is the AT&T branded version of the HD7, which is certainly plausible. Another likely candidate is the 7 Pro, which although it is headed to Sprint soon also has a GSM variant.
Either way, it looks like AT&T is getting ready for that second wave by late winter/early spring. Sounds good to us.