I own both and am wondering about the issues about rotating between them. I like the 5s for its smaller size and of course Apple Watch compatibility and the Note 4 for in meetings to use the stylus etc. They should be work fine in parallel even without the SIM due to WIFI but it's SMS/Messages that concern me. I know when you are using the iPhone and you have conversation with certain other that if you switch to a non-iPhone that you may not be able to communicate unless to unregister your phone number from Messages or turn off Messages. Even then, others may have to kill the running conversation on their side and start a new one. Thoughts? p.s. Ultimately, I am waiting for the September reveal to move to a single device.