The iPhone headphone socket has a little contact switch inside it that tells the iPhone to switch from external audio to headphones audio when plugged in. Sometimes this can get some dust or fluff underneath the contact and the iPhone or iPhone 3G can get jammed in headphones mode.
To cure this, one suggestion from Apple Technicians is to insert and retract the headphone jack a few times to dislodge the dust or fluff and clear the contacts in the iPhone.
Be gentle, you don’t want to break your iPhone or Headphones.
DISCLAIMER: We accept no responsibility if your big strong hands break your iPhone in the process. 
October 30th, 2008 at 12:33 am
That worked great Thank you!
November 6th, 2008 at 3:03 am
i tried to plug and unplug several times, i restored my iphone from itunes, i reseted my iphone with home and lock button but it didn’t work
November 6th, 2008 at 3:03 am
any soloution???
November 10th, 2008 at 9:27 am
this solution works for us… if it still goes on, maybe take the iPhone back to your local Apple Store. Don’t forget to book in with a genius first!
March 11th, 2009 at 4:49 am
If plugging and unplugging dose not work for you like it did not for me, try doing the same thing except back out the headphone jack just a little and give it a slight wiggle toward the screen and the back of the iphone while removing the headphone from the socket. It seems like the contact switch is on the screen side of the socket, and the wiggle gives a little more pressure on the switch, which in turn helps remove the gunk from inside than just plugging and unplugging. Use caution when doing so because like everyone says, you don’t want your big strong hands to break anything.
March 24th, 2009 at 6:01 pm
why doesn’t apple fix this problem?!!!! None of these things has fixed my phone, so now I have to go wait for 3 hours at the hipster bar for a ‘genius’. Just fix your product, for f’s sake.
April 29th, 2009 at 4:22 am
I am on my 3rd IPhone now, my headphone socket has gone now although it works fine there seems to be an issue with the microphone not switching on when the headphones have been removed. The wiggle trick works sometimes, there is no dust in it I can see.
1st IPhone stopped making phone calls.
2nd Switched ringer on and of at random intervals
I am seriously fed up as I have to travel 12 miles each time to get my phone replaced.