HTC Sense

Call & Control Gestures - HTC Sense

HTC wants to give you the most intuitive experience on a smartphone. That's why we've made calling-related functions even more thoughtful. And we've made finding whatever you're looking for on your HTC phone even easier with a variety of fun and intuitive gestures.

Flip to speaker
Ever realize halfway through a call that it would be better to talk on speakerphone? Maybe it's a colleague wanting to join the call or you simply want louder volume. Instead of being distracted by fumbling to find the speakerphone button on the phone, HTC Sense lets you simply flip over the phone to activate the speaker in one easy move so you can keep your focus on what's being said.

Source - http://www.htc.com/in/htc-sense