I have 4 phone paired with my RX400h and it works well.
You can use one phone at a time and paired up to 4 phones. YOu can switch within all the phones that had been paired. If you like to switch phone, you have to choose from the menu.
Every time when I start my car, it paired up and ready to go. I am not using my Boluetooth headset any more because I don't have to flight to put it over my ear while I am driving and I don't have to charge it at night.