HTC Attentive Phone is a proprietary program for WP7-smartphone HTC, whose name has a lot in common with the main functionality of it.
HTC Attentive Phone replaces some of the essential phone functions, adding to them the ideas implemented in the HTC Sense user interface for other platforms. For example, while moving the device upwards turns the speakerphone on, while in a pocket or a bag the volume automatically increases, and as soon as you take the device into the hands the device will automatically “calm” itself.
This means that those are the main four modes and your chance is to get most out of them. Just a simple chance to enjoy the presence of the HTC Sense touch into the WP7 OS.