The Shure Earphones for Cell Phones & iPods are broken down into 2 categories:
DUAL Connector which has 2 plugs at the end of the cable. One goes to your cell phone and the other goes to your MP3 or CD player (iPod, iRiver, etc). The earphones are i2C and i3C.
SINGLE Connector is to be used with the TREO 650 and 700W cell phones ONLY which play music and work as a cell phone as well. The earphones are i2Ct and i3Ct.
If you have an iPhone, only the models Superfi 4vi and Shure i2C-M are compatible with the Apple iPhone and the iPod. The Shure i2C-M is also compatible with the Motorola RZR and the Blackberry CURVE.