Wow that's a fantastic question. Since it's tied to/mimics your iPhone I think you'll have the ability to make and receive calls and texts from the watch....but will you be charged a separate roam like home fee for BOTH the iPhone and the AW4
Excellent question....Rogers reps need to chime in.
No, you currently cannot roam with your Apple Watch over cellular. You can continue to use your smartwatch with Bluetooth while travelling to make and receive calls, and to send and receive text messages.