I've just tried my Nokia CK-15W with iOS 6 on my iPhone 4S and no the problem has not been resolved.
It's a real shame, Apple have produced a very good range of phones and iOS 6 introduces a lot of excelent new features, even to the basic phone functionallity, but I'm finding their arrogant lack of response over the Bluetooth issue more and more annoying. I've complained at my local Apple store only to be told that I need to get the (non-upgradable) car kit upgraded by Nokia. I've complained via the support links on the main Apple website but have received no response and, like many others, I've written on this forum (and others) only to see no response whatsoever from Apple.
What is worse is that the brand new Blackberry provided to me by work functions perfectly with the car kit as does my girlfriends' HTC.
The question here seems to be how do we get Apple to recognise this as a problem? When iOS drains the battery it gets publicicy and is fixed. When iOS collects GPS data and syncs the file with iTunes it gets publicity and is fixed. How do we get the same level of publicity for Bluetooth?