I cant hear people iPhone 3G

2 days ago after i installed the new update 3.1.2 i cant hear people speaking to me but they hear me,its all start when i were listing to some music with my earphone. i try to reset all setting and still dont work, the only way for me to talk with my phone is with earphone only.
i would like your guidance and help will be useful to me.
Hanan, Israel.
iPhone OS 3.1.2 Windows 7