Exact same problem with 2007 Lexus (Toyota made) ES350. I turned off Siri and had the same problem with direct voice dialing via pushing the button. I have done the deleting on both phone and vehicle- same problem. No issues till IOS 8. (8.02). After hours of obsessively trying to fix, I did notice a few issues:
1) on occasion, the phone takes over the entire navigation system screen which the Bluetooth is combined with and I have to manually hang up.
2) On occasion the phone interface on the car show the Bluetooth the connection with 3 bars, but say "out of range".
Last oddity- late yesterday night after deleting all Bluetooth devices from the phone and vehicle Bluetooth registration profile, I did make several successful calls through Siri. This morning back to the same problem. Call terminated by network.
I hope this bug will be recognized and addressed by Apple quickly. I can connect with a a ten year old Motorola but not with my iPhone 6 Plus. BTW I tried this with an updated 5S as well as an iPhone 6 and they all have the same problem -So the problem isn't the individual phone or vehicle.