hard wired hands free, change holder?

[Tupe]

I have a car that has a Nokia branded phone holder as part of the ( I presume hardwired) hands free kit, there are certainly two wires coming out of it into the dash. My question is:clearly built for a narrow Nokia phone, can I change to holder itself with impacting on the rest of the system, or do I need just to buy a new system and have it installed. I have no idea if the current fitment works, not having a narrow nokia phone......
thanks in advance