Ringing through blue and me has never worked for me with the iPhone 4. You can still answer it through the steering wheel and then it will cut out the radio so you can make the call.

mine works spot on, make sure you are running B&M 5.5 and you have the latest apple firmware, think its 4.2.1, once youve updated the software, delete and re pair the phone from both the car and the phones paired devices, should work a treat then