Don't hit your phone. Don't put anything other than an earphone in the jack. Definitely don't dissasemble the phone.
Press and hold both the home button and the power button until the phone resets with an apple. After about two minutes the phone will restart. You will need to do this two or three times. Each time your phone will react slightly differently. Don't be surprised after the first attempt if you loose both the mic and the speaker. Check the phone each time by having someone call you. THIS IS A SOFTWARE ISSUE.....NOT A HARDWARE ISSUE and the amatures on the web would have you believe. I admit rarely....rarely it may be hardware. 95% of the time this will fix the issue. This occurs on both I4's and I5's.