The WiModem works with the VIC-20, C64, SX-64, C128, and should work with the Plus 4 (I just got one in to test). I knew the PET didn't have power available, which is why I didn't bother adding it to the compatibility list. With power added, it should also work. The Plus 4 and PET might need the UP9600 hack disabled, something you must do when using it in C128 mode.