What happens when you reset the network settings
My ringer is not working. Will not ringer, only vibrates. What will happen if I reset the network settings?
iPhone 4S
Did you check the "mute" button located on top of volume buttons?
Reset network settings option will reset all network settings, including passwords (excluding passcode), VPN, and APN settings.
Just to give you an idea.
http://www.apple.com/support/iphone/assistant/wifi/#section_5