Why won't these devices be backwards compatible? Very curious. Physically the same wires are used for BC, so it has to be in the USB stack then? Lack of BC with USB 2 OHCI/UHCI?
I'm afraid I don't know enough about it but it seems to be related to audio devices. The USB transport I have is called the M2Tech Hiface and it has a very advanced asynchrous USB protocol with the max 480mbs used of usb2 for 24 bit 192khz audio, it won't work with the USB 3.0 NEC chipset. The MagicJack phone I imagine is also a fairly advanced protocol and it won't work either. When you plug either in the driver loads up but thats it, no sound.