Seriously, this question hasn't been answered yet? I logged on this morning for this.
I know. Gotta be someone with an ATT microSIM to put into the LTE Verizon iPad to see if HSPA works.
Crazy no one has posted yet, considering some Walmart's sold a few iPads are midnight and it's 830AM eastern time, past the 30 minute official Apple retail store launch.
If no one posts, I will get my Verizon iPad LTE when I get off work later this afternoon and put my ATT microSIM into the iPad to see if it works.
Also I will put my Verizon Galaxy Nexus unlimited LTE microSIM into iPad and see if I get LTE/3G CDMA data off the microsim. Verizon doesn't audit LTE microSIM in tablets (that are from the LTE phones). So that would give me maximum flexibility to keep my Verizon LTE ipad.