In short the answer is no, I've made enquires along the same lines myself. Your sim card is your phone number so without swapping your card over each time you get out the car you can't do it. Best remedy I can think of is use one phone to forward or divert your calls to another, if they're both on the same network and contracted, chances are the forward or divert will be free. If you're on different networks you may have to pay. eg. Give everyone your 6230i number, leave it in your car and then set it to forward or divert calls after say 3 rings to your other phone! That'll give you chance to answer it if you're in the car and divert it if you're not.
I'm curious why you'd want a phone with better facilities than a 6230i. I have a small business and have a lot of 6230i's on contract and wouldn't swap them for anything. They are internationally renowned as the best business phone on the market, maybe not "cool" enough though because they don't flip or slide perhaps?