Your car stereo is probably another brand pretending to be whatever Subaru put in. Once you find that out then it will work. The only difference in the car kits is one wire. Its the same wire that is used for a CD changer to be used in the car so providing you have a CD changer possibility in your car it should be possible to get it to work.

EDIT: Here is a link to what you want.

Here is the information about iPhone compatibility.