I have a 920XT and a E1000 when I try to sync my E1000 I get a screen saying
How to Connect...
In order to connect your E1000
you will need to disconnect the device that is currently connected.
HOW DO I DISCONNECT MY 920XT WITHOUT FORGET DEVICE?
I have found no way.
Besides the Iphone should be able to connect to both devices one at the time, since the 920t is not sending any data and is already synced.