Mobile Phone Car Kit Advice required..... [Simon Clark]

hi all the current mrs clark and i have both had Nokia 6310 phones for years now (and previously the similar, but older range). we have desk chargers, spare batteries, us voltage chargers etc etc. we accept that we will have to upgrade eventually as the current handsets are crumbling and ebay prices for replacements are increasing! the main issues are the car kits. she has a mercedes with the holster in the glove box and i have a standard Nokia cradle, both obviously integrated into the car audio system etc. we want to stay with Nokia. we want to be able to jump into each others cars. we would prefer for the handsets to be charging when we are in the car....