I have a 2008 Nissan Altima, which shares the same bluetooth hardware as the Infinitis from the same time... I am also having issues. The phone pairs and connects fine... the calls even go through. But, the audio is all garbled.
This happened to me when I had a G1 many years ago. And, after researching it then I am fairly confident that this is a bluetooth protocol issue. Whether it be through oversight or a mistake (hopefully it wasn't a design decision) the backwards compatibility protocols for certain older bluetooth systems apparently didn't get done correctly.
Sure, ICS will work because they got the protocols correct on that version... so my hope is that it gets fixed at some point with an update to JB. Now, I'm with Verizon so I don't know if this issue is carrier specific, or OS specific... that could help narrow it down if we could figure that out.