As you are probably aware iPhone owners upgrading to iOS 4 have been experiencing quite a few problems], such as a seemingly never-ending backup procedure, however we are hearing of one very annoying problem which some users have noticed since carrying out the update.
If you connect your iPhone to your car stereo via a USB lead you may want to hold back on installing the update to iOS 4, this is because there have been multiple iPhone owners complaining on Apple’s support forums, suggesting that this functionality is no longer working.
You can see the thread in it’s entirety here, the person who started the thread stated that when he plugs his iPhone into his Pioneer car stereo it says “Not compatible”, despite it working fine with previous iOS versions.
Another person on the forums states that songs go back to the start after receiving phone calls or switching the engine off, I can imagine this issue becoming very annoying over time.
There are a couple of workarounds which some users are claiming fixed the problem (see these via the source link below), however I would imagine that different stereos require different workarounds, and with there being so many stereos out there this is going to be a hard problem to resolve.
As we hear an update on the situation we will do our very best to keep you informed. If you have been affected by this problem please state which car stereo you are plugging your iPhone into.