That was quick- from rumor to official post on the HP-Palm blog. The HP TouchPad is officially coming to ATT with 4G ( we assume HSPA+) as the HP TouchPad 4G. No mention of a date or price yet. The tablet's Snapdragon will run at 1.5GHz vs. 1.2Ghz for the WiFi only model (the Qualcomm dual core CPU used in the WiFi model has a max clock speed of 1.5GHz, and it looks like HP underclocks it to 1.2GHz).
The HP TouchPad 4G on AT&T will have 32 gigs of storage and will otherwise be identical to the WiFi model that came out on July 1.