I Can't Hear a Voice on the iPhoneby Crystal Bonser
When speaking to someone on your iPhone, the sound you hear is transmitted through the receiver. If your receiver is not transmitting sound, external accessories may be interfering with sound output or the mesh over your receiver may be clogged. Of course, sometimes issues like these are simple glitches that can be corrected by resetting or restoring your device.
If an accessory is connected to your headset port, such as a headset, headphones or an adapter, your call sounds will be transmitted through the accessory and not your receiver. This also applies if your Bluetooth setting is turned on and a Bluetooth headset that is paired with your iPhone is nearby. You can correct these issues by removing all accessories from your iPhone and turning your Bluetooth settings off in your iPhone's "Settings" menu.
Clogged Headset Port
If your headset port is clogged with debris, your iPhone may act as if an accessory is attached even when one isn't. In this case, your call sounds will not be transmitted through your receiver. To clear the clog in your headset port, place a headphone jack in the port, pull it out and repeat several times. If the clog is severe, you may need to have your iPhone serviced.
Clogged Receiver Mesh
Another issue that may be preventing you from hearing sounds through your receiver is a clog in your receiver mesh. Since your iPhone's receiver and the mesh that covers it are quite small, it doesn't take very much debris to clog it. This problem can be corrected by gently brushing the receiver mesh with a small soft-bristled brush that is clean and dry.
Reset or Restore
If all else fails, try resetting or restoring your iPhone. To reset, hold down the Sleep/Wake button and the Home buttons at the same time until the Apple logo appears and your iPhone restarts. To restore, connect your iPhone to iTunes, then select "Restore" from your iPhone's "Summary" tab. Make sure to back up your contacts when prompted to do so because this process will remove all data from your device.