Iphone 3g sound problem

hi guyz

i got a major problem with my iphone 3g sound and before you reply search on the forum ive searched the entire internet and none of the solutions work for me that y im askin

the problem is that sometimes i dont get sound, no unlock/lock, application, message sound whatsoever. I cant even take a call . ive tried doing the following and this happens:

1)play music from ipod and it just doesnt play. play button goes back to "play"

2)start soniclighter app and it says phone or microphone being used and shut it off before using this app

3) app "i am t-pain" doesnt start just goes back to the menu

tried plugging in the headphones still dont play any sound!

also sometimes when the sound is working the phone will auto hang and i have to restart and no sound again!!!!

i bought my 3g second hand and when i got it none of these problems were there after i jailbroke it myself this stuff started happening!

is it software or hardware??? any solution??? ive already tried evry solution on the internet !!

tried restoring to different firmwares multiple times sometimes sound works sometimes it dont
but all the time when it starts working, it stops working again after restart, etc

sometimes when i leave the phone off for an hour or more and then start the phone it starts working again, but even with that trick it dont work all the time!

any suggestions?

ok i got it repaired and they replaced the ringer unit or sumthing and now its fixed!