iphone 4 dialer not working

hi i have an gsm iphone 4 and whenever i try to use the dialer at it freezes and my phone becomes unresponsive. it happens wether its jailbroke or not. any idea what may be causing this? ive restored it 5 or 6 times. its weird itll work for 4 or 5 seconds then freeze then itll go to an all black screen and wont do anything even if i attempt to reset it or itll go to a white and grey screen. i either have to let the battery drain or remove the battery to make it work again. but no matter what i do i cant use the dialer. even after i do a completely fresh restore without syncing anything it still wont work. i bought the phone off craigslist so i dont think i could take it to the apple store. anyone have any idea what to do to fix this?

 

would apple give me a replacement? i bought it second hand off some guy off craigslist. i dont wanna bring it in to apple and get charged for to have to get a new one. i dont think its the jb causing it because even with stock os it wont work.