From the BMW installation instructions, below is the fitment text.
3 Series Sedan (E90): Select Vehicle Production 03/05 - 02/09*
3 Series Coupe (E92): Select Vehicle Production 06/06 - 02/09*
* Vehicle must have optional alarm pre-wiring (SA 5GA), which is 100% option for US spec vehicles.
You can check your options using http://bmwvin.com
using the last 7 digit of your VIN to see if you have that option.
I've also attached the BMW installation instructions and the e90 forums instructions for your review.
Price is $270.
Let me know if you have any other questions.