Bluetooth Integration Kit
 

Grom Audio Bluetooth adapter for sale. This connects directly to the back of a RX8 OEM head unit and allows you to connect your phone wirelessly to listen to music or answer phone calls, all while retaining steering wheel controls to skip through music. It includes an aux cable to use non-Bluetooth devices and a mountable microphone to talk on the phone.
$100 bucks plus shipping, definitely worth it of you don't want to invest in an aftermarket deck

Mazda RX-8 2004-2008 (radio firmware v9.55 or later /v10.1 and v9.81 not supported/)

probably priced to high. amazon has it for $80 shipped.