There may other differences but those are the most notable ones we've seen so far. With the addition of the 1900 WCDMA band, the HTC Titan can finally reach AT&T's "4G" HSPA+ network, giving a nice boost to your upload and download speeds. Generation one devices were HSPA, meaning 7.2Mbps while second-generation Windows Phones on AT&T feature HSPA+ aka "4G", which is theoretically possible of 21Mbps (but on AT&T, it's rare). Forgetting nomenclature, does it make a difference? You betcha.
More of their first thoughts here.