I don't know if it will cost a lot of money if you opt for pre-wired instead of non pre-wired... but if you can change it and it won't cost too much extra, I think it could be worth it.
If you should decide - anytime in the 'near' future - to retrofit a phone kit in your car, then you won't need another rear view mirror with microphone and other additional wiring... which will make the phone retrofit more expensive.
As far as Bluetooth is concerned: I know there are UHI and MHI phone kits available right now. MBenzNL offers them as well: the kits themselves do not support Bluetooth, but some of the GSM phones which are compatible with these kits do have Bluetooth capability.
The kits are original MB.
greetingz,
BigSis