I have the F20BT, which I understand is the Australian version of the Z120BT. I also have two iPhones, one 3G and one 3GS, both of which seem to work perfectly once synced, the issue I have is that about the switching.

If I preference my phone it works fine, if I preference my wifes phone it works fine. The problem is that if my phone is preferenced the system will NOT hook up to her phone, even if I'm in another state (and vice versa). Seems I have to manually change which phone will be connecting.

To be 100% clear, there is only one phone in or near the car at any one time, so it's not the system connecting to the wrong phone or getting confused, it just will not connect unless that particular device is set as the primary phone.

Has anyone else had this problem or is there a solution other than manually switching when needed?

is there a solution other than manually switching when needed?

No.

The manual says it can connect to "up to 5" devices and the manual talks about "Setting for priority connecting" which seems to say it should connect to any registered phone with a preference for which ever one you choose IF there is more than one phone in the car.

It's a bit of a disappointment if really can't do that.