According to MobileCrunch (who seem to be taking credit for some strange reason), HTC said:
The vast majority of devices we launch after Hero will have a 3.5mm jack. Devices that we have already announced but that still come out after Hero will not necessarily be a part of this change.
This obviously excludes the new HTC Touch Pro 2, Diamond 2 and HTC Snap,but we can look forward to 3.5 mm headphone jacks on the HTC Whitestone, Firestone, Star and Superstar at least.
Read more at MobileCruch here.
Thanks itsy for the tip.