Alpine used to make steering wheel modules to work with their head units. I.e. you require your existing one to work with the Alpine head unit.
Or you also have this option.

Or.. look into an audio processor.. Like a rockford three sixty..
ROCKFORD FOSGATE 3 SIXTY : Maroochy Car Sound
This is the best way to intergrate with stock components.

You might have got it sorted but if anyone reads this...
I got an ipod/iphone adapter which plugs into the back of my head unit from Neo Car Audio :: The leader in OEM integration. Used it in my sp23 and i have now installed it in my 3MPS and it works a treat, charges my phone to.
Looking at your phone to change the track while driving is dangerous.