I recently had problems with my 6230i and thought about changing it but I was told in the o2 shop that the newer phones will no longer work with my existing car kit. I ended up getting the phone repaired despite the fact that o2 said it was unrepairable due to water damage!
You may have to upgrade the car kit aswell as the phone if you wish to change.
Most Nokia phones work with cradle car-kits. If I understand your question correctly, I think what you need to discover is which phone, apart from the 6230i, works with YOUR car kit.
As a general rule, the 6xxx series of Nokia phones use the same cradle, so if you look at other phones in this range, you should be OK (look at the pins and connectors at the bottom of the phone if your retailer can't help). For example the Nokia Advanced Car Kit CK-7W, which I use, is compatible with a number of Nokia phones, including the 6230i, without having to change the cradle.
I asked the question really because I was led to believe that carkits are being phased out due to bluetooth.
My husband and I use the same phones/kits for both our vehicles. I need to get a new phone and as the 6230i is now unavailable I am trying to find a phone thats compatible.
Not true - the car-kit I have has a cradle (for charging) AND the option to use Bluetooth, which I do for sat-nav as it allows me access to my phone's address book.
Check the Nokia web-site, they are still on offer. At the moment, AFAIK, Bluetooth technology doesn't allow a phone to recharge its battery - in fact it does the opposite by running the battery down faster!