The problem with getting a new radio, is that this functionality isn't always available in the new radio so you have now defunct buttons on your steering wheel.That is, unless, you spend a lot of money on a compatible radio.
I have a Sony xplod CDX-GT110 which does.t have this functionality, but it's bigger brother CDX-GT270 does have this.
In face, many of the stereos, CDX-GT35 CDX-GT130 CDX-GT330 CDX-GT440 all look the same(ish) but do not have this functionality
It seems if you don'y have it, you don't have it.... or do you?
Philips screw driver
Soldering iron and Solder
3.5mm adapter socket
Hook up wire
(RCA plugs for Aux out)
Step 1: Disassemble
Then remove the screws holding the CD player and lift this out of the unit - taking care as it lifts out of the connector.
Remove all the screws from the back heat sink panel and the front panel so you are left with just the board in the bottom chassis.
Remove the silver screws and carefully lift the main board from the metal chassis.
Step 2: Locate the missing connector spaces
This is where you add your desired functionality.