I've had my iPhone 5 for 3 days and the speaker problem started on day 2. The caller can hear me but I can't hear them on the internal speaker, I have to use the loudspeaker (hands free) to hear them. Tried restarting and rebooting the phone but still have the same problem. Need to take it in to apple for repair which is really annoying. Anyone else found a fix for this?
go to setting / general / cellular , switch off cellular data / enable 3G , after that wi-fi off .
make a call , all in order
now enjoy update iOS 6.1 REALEASED 28 JAN 2013
NOW INTERNAL SPEAKER IS OK