this isn't a hardware fault it's caused by a dirty/faulty charging dock (9 times out of 10) it's just dirty i have had this in the past took it to apple and they use a very small light paint brush to clean the followed with a thin hard paint brush to get off more then he used a circular metal object to finish would recommend you do the last yourself though but it's on the apple support forums aswell but you will have to find the link yourself
not gonna start breaking forum rules ;-)
its not true... I tried to restore my phone twice but still no volume bars hahaha its bug in ios5.1..... No one know here how to fix our problem. All reply in this thread is not helpful