The (mobile phone) situation in the US is different to that in Europe, but something happened to me in my 2001 car with a factory-fitted phone kit that was similar in effect to what you are describing. The cradle was suitable for a variety of Nokia handsets, this being fine as Nokia has the biggest market share. However, about a year later Nokia's principal new phone (6310i) did not fit anymore, despite having a '6' prefix.
Equipment modification would have cost GBP 250 (Germany) or GBP 400 (UK). I was outraged.
Even though it wasn't entirely MB's fault, fortunately my (German) dealer found a way to do the upgrade FOC as a warranty issue... :-)
I had to arrange a drive to Germany from London, as I had bought the car there. It took a few months to find the opportunity but it was no hardship.
Have you contacted MB US? Try the marketing director.
DAS