You would need to paste what you are typing, but I expect you are typing:
Which will give you the error you are seeing. First, that is incorrect. Second, tty.Bluetooth-Modem is incorrect anyway. The D4i is not connecting via bluetooth. Follow the instructions closely. Start by typing:
Paste the results here so we can tell you what the correct device to use is. Also, this is all kind of secondary - what is the actual problem you are seeing? Maybe you just need to go to Preferences -> Advanced -> Scan For Serial Port and choose the correct one.