I found out that Apple is assembling a new headphone jack flex cable w/ buttons. There are 2 different part numbers. The older one is part no. 821-0449-09 and the newer one is no. 821-0600-A. They are NOT compatible! If i assemble an older cable in a newer iPhone, the iPhone get no sound from speaker. After inserting the headphones, no sound from the headphones but sound from speaker.

did anyone get this problem? And anyone knows the difference?

Thanks

Ive got the same exact problem. I cant seem to find the flex cable that is compatible with my iphone.

the temporary solution I had for the sound problem was, I cut off the headphone jack of some old headphones I had, and put in in the headphone plug in the iphone. Sll the sounds come out and I can make phone calls, but i cant listen to music.

i've got the same problem. is there anybody with a solution?

OK
I have had this on two repairs to iPhones. This is the solution if you have been supplied with the wrong part (and let me say the correct part simply is not out there on the market).
The problem is that the small contact breaker at the end of the socket is wired the wrong way round - this is how to botch it without breaking anything.
At the end of the black headphone socket, there is a small band of copper which forms part of the switch that is moved when the jack is inserted. You need to use a sharp tool (tip of a blade) to gently slide this copper part slightly off the end of the black plastic housing at the right hand side. You are trying to get this copper band away from the contact which is just inside the socket on the right hand side. (look inside the end and you will see the simple contact breaker)
Once this is 'just' clear of the contact, use your sharp instrument to bend the internal contact part so it is on the other side of the copper band part of the contact (you are bending the small internal contact towards the opposite side of the socket i.e. almost into the mid point of the hole).
Now, gently slide the external copper band back into place so that the internal contact now sits on the left hand side of this part. Test the contact breaker now using a headphone jack. You will find it tight the first couple of times you push it home, but it will be fine, even after several months of use my contact breaker is still working fine :-)
Your iPhone will now play through speaker when no jack plugged in. It now recognises headphones and your volume button no longer says 'headphones' when they are not plugged in...
So, if all is well, and it should be, use a tiny dab of superglue on the external copper band on the top section just to make sure it stays where it should in future as you don't really want to go back into the casing again do you!

One of my friend in sweden fixed this problem by modifying the one with part no 821-0449-A. He compared the two flexes and revise the old one to the new one.
He has maken several pcs, but it's not easy.
Hope some one can test it and post a guide.

It seems the solution proposed by our colleage scudder is the more reasonable I found so far in many forums at web. I will try this one... I bought 3 parts at ifixit.com and all of them I got the same problem.

when I have done i will post a reply...

Running into the same issue. Anyone post back if the above fix worked or not?

I just got off the phone with a repair shop in the states that has several of them (he verified over the phone that they are 821-0600-A) for a reasonable price. I will post up their info once my part comes in and I can confirm that it is the correct part.

Got the part in and it worked perfect. Good price too!!!

Please let me know where you found this part. I need one. THANKS!