Someone at HTC decided that having a dedicated 3.5mm headphone jack would be a waste of space, and indeed it would be. So they use ExtUSB, which is compatible with some miniUSB cables (like those for charging and syncing). If you have an HTC device (such as the TyTN, TyTN II, Shadow, Touch, Wing, Advantage, etc), you can buy an inexpensive $5.00 converter that will let you use any standard headphones with your phone. Click on over to Amazon to see (and ignore that it says Touch Dual, which also uses ExtUSB).