Use an Apple Watch Series 2 or 3 standalone with an Android Device?
YES...You Can use an Apple Watch Series 2 or 3 standalone with an Android Device!
Here are the steps that I used (it is NOT necessary to initially have a SIM in your iPhone when setting up. I am using a Series 3 GPS Only AW with an older iPhone 6+ on iOS 11):
You MUST Own an iPhone [for Apple Watch Series 3 (GPS) or earlier models of Apple Watch, you need an iPhone 5s or later with the latest iOS] in addition to your Android device and have Hotspot functionality on your cellular plan.
1) Turn on the Hotspot on your Android device (I'm using a Note 8).
2) Connect your iPhone’s wifi to the Android phone's Hotspot.
3) Your Apple Watch will access the internet using the wifi hotspot connection on your iPhone.
4) Now that you have “established” an authorized/known (can’t think of the word Apple uses) wifi connection you can leave the iPhone at home and either leave the hotspot running or turn it on when you need updates to certain apps on your watch!
5) Go into messages on your iPhone (especially when the SIM is NOT in it) and be sure you have an email address that is checked off to use with iMessage. I used iMessage seamlessly - with voice text entry…too small to type (of course there is no trail of the SMSs on your Android phone).
My weather updates, mail comes in and I can respond. Haven’t tried anything else except Siri who told me the time but couldn’t answer a couple of questions about Apple Watch (just referred me to open the web on the iPhone).
Surprisingly, I didn't get much of a hit on the battery either in my Note 8 or on the Apple Watch when I left the Hotspot on. Not sure how much data was used but I get a 10GB/month hotspot on my AT&T plan so doubt I'll eat that up before the next bill comes out.