unable to hear clear sound of your cell phone

Can't hear phone calls unless it's through rear speaker or headphones

 

How do I solve the problem of not being able to hear phone calls unless I'm on "speakerphone" or have a set of headphones plugged in?

I think the problem started a few days ago when I was listening to some music through the headphone jack. Ever since then (I don't use the phone much, so I'm not certain) I haven't been able to take or make a call without using speakerphone mode, or plugging in some headphones. When I unplug the headphones, I can't hear anything through the front (screen side) speaker that's normally used for phone conversations.

I've tried plugging in and unplugging a set of headphones over and over again, hoping it would switch back. But, I haven't had any luck. I've tried a hard reset as well, and that hasn't helped me either. I'm willing to open it up and see if I can fix it, but not sure what I'm looking for. So, I'm hoping someone can help out. If all else fails, I have an EVO 4g I can use until I'm due for a new phone.
I'm sure this has happened to others before. But, searching for "phone speaker" doesn't bring up much useful stuff (I'm not good at searching the right terms I'm sure).. 

solution :
please take a pin slowly clear the dust of the ear piece steel cover and wrap the pin slowly . please do not put the pin in side of the steel mesh.just touch the steel mesh and the clear the dust and dial 123 or 121 to listen the sound.OK its clear...