As many of you have, I lost the ear hook on my Sony Ericsson HBH-660. I contacted SE Customer support at (866) 766-9374 (for the U.S.) and spoke with a friendly rep named Jen who offered to send me a replacement despite it not being covered under warranty. She made it clear that this was being done as an exception for me, that this was not the norm, and that it would be done for me only once. I'm sharing my experience in case anyone else would like to try. She also mentioned that the part could not be ordered, but my ear hook came with a receipt, which conveniently has the ear hook part number:
SXK1096028/1 HBH-660 Ear Hook

This part number may end up being useful if we ever find a vendor who can order the part.

Conrad

keywords: HBH-660 Earloop Ear Hook