Are they simply stored on the HTC phone or synced with an Exchange type service?
If they are simply on the device, the easiest way is to sync them either with a support app on your computer and them import to the iPhone or sync to an Exchange type service from the HTC phone, then do the same on the iPhone.
This document covers what can be synced on the iPhone and the supported apps on the computer.
Im having same problem to be fair. They are all on the handset and Im completely lost as to how I get them sync'd and what to snc them with as I done a few google searches and it suggested outlook express which isnt available on Windows 7 .....
Just seemed anytime I tried to import from memory card on HTC Desire to even a googlemail account it just seemed to duplicate them in my contacts list on HTC .....
Would be grateful if anyone knows an idiot proof step by step guide on how to get your contacts from HTC Desire to Iphone4 iso5
Thanks In Advance