bhome83: The HF3 has a 3-button remote and a microphone. The 3-button configuration integrates volume up/down and is designed for Apple product use only. If you are using an iPhone, it must be 3GS or later to make use of the volume controls. The center button on the remote is your end/send, play/pause, track forward/back button. A list of compatible Apple products can be found on our website at http://www.etymotic.com/ephp/hf3.html.
If you are using another manufacturer's device, the HF2 with single button control is a more universal solution. If you have no need for the microphone and controls, the HF5 is an earphone only that uses the same drivers as the HF2 and HF3.
Also - the MC3 (moving coil series) also incorporates a microphone and 3-button control for Apple products for $99. Additional information can be found at http://www.etymotic.com/ephp/mc3.html.
The HF2 and HF5 currently have a factory authorized sale: $149 for the HF2, $129 for the HF5.
Hope this helps!