I have an Apple Watch 4 w cellular that I purchased at Verizon. We're currently considering switching all of our phone lines to AT&T, and would get new phones but I would want to switch my existing watch from Verizon to AT&T. Is that possible? I've read that the watch and the phone it's linked to need to be with the same carrier, but haven't been able to find out if the watch comes unlocked for any carrier, so to speak, or if it will only work with Verizon. Thanks in advance for any info!