I have the same issue, the phone does not ring on incoming calls, moreover, when changing the tone I can't hear the new tone, and when I press the keys on the
keyboard I can't hear the clicks, if I use the headphone I can hear everything.
I checked the silent switch, it is not silent, and I restrat the phone, no help.
I have this issue immediatly after purchase and unbox
the phone is updated to 4.3.3
note: I use the same computer to sync to ipad.