No matter how loud you speak, the person on the other line cannot hear you.
Before completely taking your phone apart, it may just be that your mute button has been pressed. By pressing it again, it will unmute it.
If your mute button has not been pressed, it is likely that there is an issue with one or more of your microphones. If this is the case, you will need to open up your phone and replace the microphones. Remove the microphones by using this guide.
You cannot hear your phone conversation.
Your volume may be turned down. To ensure this is the case, press the + key on the volume button.
If you are having an issue with the audio on your phone and there does not seem to be a problem with the volume button, your Internal Speaker may need replacing. By using the back housing replacement guide, you can open up your phone and check out the internal speaker from there.
There does not seem to be a problem with the audio speaker, but when you receive a call there is no ring.
Underneath your phone there is a switch to shut your ringer on and off. It is possible that this switch may be on the "off" setting.
The keys on your keypad are unresponsive or stick.
This will generally require that you open up the phone and either clean the connections between the buttons and the motherboard by using this guide or replace the button pad altogether. You can find help replacing the button pad here.
The LEDs signal phone status and other controls include a ringer volume, speaker volume and microphone mute. If you are having a hard time seeing them, there are some possible solutions.
If you look closely, there should be three small plastic reflectors sticking out of the top of the phone. If any of these are missing, the light bulb will not shine as bright. If this is the case, you may need to replace it. You can open up your phone with the back housing guide and check it out.
If you cannot see any light at all, the bulbs may need to be replaced.