Actually...that model Pioneer does NOT have the telephone mute option. Although all is not lost.
You can add the feature for about $5 extra bucks
You need to go and make a purchase of a 5pin relay and make sure that the relat has pins 87 and 87a. A pair of 87 numbered pins will not work.
Cut the accessory wire going to the cd player and put the end that goes into the cd player to pin 87a. Now, the accessory wire coming from the car needs to goto pin 30 AND pin 85
You will now put the radio mute wire from the car kit to pin 86 and hey presto whenever your phone rings the radio will SWITCH OFF it won't pause it it will completly switch it off and then switch it back on when you hang up. I know this isn't as good as simply muting the radio but hey...I can work miracles...the impossible takes me a little longer.
Oh yeah...btw... you will have a spare pin left over on the relay (87) put a spade connector over it without any wires coming out of it to make sure that it doesn't earth out aginst the body of the car and pop the radio fuse.