Samsung GT-I9100 User Manual page 30

 Ensure that you have not set call barring for the phone number.
Another caller cannot hear you speaking.
 Ensure that you are not covering the built-in microphone.
 Ensure that the microphone is close to your mouth.
 If using a headset, ensure that it is properly connected.
The phone beeps and the battery icon flashes.
Your battery is low. Recharge or replace the battery to continue using the phone.
The audio quality of the call is poor.
 When you are in areas with weak signals or poor reception, you
may lose reception or experience poor audio quality. Move to
another area and try again.
 When you are in areas with weak signals or poor reception, you may lose
reception. Move to another area and try again.
You select a contact to call, but the call is not dialled.
 Ensure that the correct number is stored in the contact list.
 Re-enter and save the number, if necessary.
The battery does not charge properly or sometimes the phone turns itself off.
 The battery terminals may be dirty. Wipe both gold-coloured contacts with a
clean, soft cloth and try charging the battery again.
 If the battery will no longer charge completely, dispose of the old battery
properly and replace it with a new battery.
Your phone is hot to the touch.
When you use several applications at once, your phone requires more power and
may heat up.
This is normal and should not affect your phone's lifespan or performance.