I can hear a caller but they cannot hear me...muted I think. Hoow do you unmute?

Your mouth piece microphone needs to be replaced.

You may have accidentally pressed the Mute button. Undo as below
Mute a Call:
You can talk to someone nearby without letting the caller hear you during a call. During a call: Press <C> t o mute the microphone and "MUTED" will display on the LCD.
Your caller cannot hear you. Press <C> again to unmute the microphone.

check that if your volume is mute
if yes unmute it and the caller hear you soun clearly

Here are a couple of things you can try. I included the link for the user guide below.

Callers cannot hear me.
• Headset is muted. Press the mute button on headset to unmute the microphone.
• Headset microphone boom aligned incorrectly. Align the headset boom with your mouth.
• The USB adapter is not set as the default Voice device. Use the Voice settings in Windows under Sounds and Voice Devices to select "Plantronics C610/C620" as the voice device.

Here is a link to the Plantronics C610 User's Guide.

Good luck from Headsets Direct!

Look to see if it is Muted. Remember if it says "Unmute" it means it IS muted. Push the button to unmute it. Sometimes it gets bumped accidentally...

Take your phone off of "UnMute". It may seem a little backward at first. When you see MUTE on the screen, it is giving you the opportunity to mute your phone. In other words, you're good. If it says "UNMUTE", you have muted the phone. All the stuff in the previous post is a little over the top.

Tap both the top and bottom (up/down) at the same time - you should be able to hear the mute tone, and then you're unmuted. Muting works the same way.

Check out this link below to download a PDF manual, software, and more for your phone. Just copy and paste into your browser.

http://www.lge.com/us/mobile-phones/LG-CU720-Red.jsp

Page 26 of your manual:
Muting the Microphone
In open the slide, you can mute the microphone
during a call by pressing the left soft key
[Mute]. The handset can be unmuted by
pressing the left soft key [Unmute]. When the
handset is muted, the caller cannot hear you,
but you can still hear the caller.

Hope this helps, let me know if I can do anything else for you.
JimmyC

Check out this link below to download a PDF manual, software, and more for your phone. Just copy and paste into your browser.

http://www.lge.com/us/mobile-phones/LG-VX8500-Pink.jsp

Mute Function and other sound adjustments from page 21 in your manual.
The Mute Function prevents the transmission of
your voice to the caller. To quickly activate Mute
touch Left Soft Key [Mute], then to unmute
touch Left Soft Key [Unmute].

Hope this helps, let me know if I can do anything else for you. Don’t forget to rate me or leave a short not. I appreciate it. Thanks.
JimmyC

Receiving Calls
1. To answer a call, touch or open the slide.
 If the slide is closed, simply slide it up.
 If the slide is closed, press the Voice
Commands key twice, then touch .
 If the slide is open and the touch buttons are
lit, touch .
NOTE If you touch Left Soft Key [Quiet] while the
phone is ringing, the ringing or vibration is muted
for that call.
NOTE If you touch Right Soft Key [Ignore] while the
phone is ringing, the call will end.



Mute Function
The Mute Function prevents the transmission of
your voice to the caller. To quickly activate Mute
touch Left Soft Key [Mute], then to unmute
touch Left Soft Key [Unmute].

NOTE! while doing this you must call someone then while talking with him touch Left Soft Key [Unmute] to Unmute

Hope it help you out ^_^
try download the manual if you loose it
http://www.cellphones.ca/upload/manuals/lg-vx-8500-manual.pdf