What is this?

[AeolianReflex]

What is the hole on the upper left side? It looks the same as the microphone hole but it's not listed in the manual. All the cases I've checked out have a cut out for it. Just curious...

 

[Harry2]

My One X has there hole with the noise cancellation microphone.

I'm not shure, but I think the Rezound has this too

EDIT: Yes search in The Verge review for "noise cancellation".
http://mobile.theverge.com/2011/11/14/2557172/htc-rezound-review

Harry

 

[zazan]

It is a noise cancellation mic.

 

[Cares]

Yes to noise cancellation. When you're talking on the phone and you have your finger over that hole rubbing around...it will make you sound muted to the other end. Keep it clear when talking on the phone.