Correct, as is airplane mode
I think someone in the Mojo thread mentioned that the interference really occurs on 2G and is not noticeable really on 3G/LTE.
I do get some WiFi interference with my DX100 DAP so I am not surprised that the phones being so heavy weave generators may impact the audio signal.
I never got any interference with my Note II on the Mojo. I didn't set the phone to Airplane Mode and received all the usual push message and downloaded updates etc all the while.