The two versions of Earset are:
Earset 1 home. This has a specific plug fitting to connect directly to BeoCom6000 or BeoCom4. No other adaptor is needed for these models.
Earset 1 mobile. This has a 2.5mm stereo jack plug and requires one of several adaptors available from Bang & Olufsen to make it work with a selection of other brands of mobile.
If the Earset you purchased off eBay has a jack plug, it has been described incorrectly. It is a MOBILE version NOT HOME Earset.
Hope that helps.
Opman