Having an alternative phone is fun. I've had many throughout the years.

The problems start when you need to interact with others. Like your bank, which only has the login app in the Android or iPhone Store. Or your local transport app. Uber, your library, Starbucks, etc, etc. Or 2FA for various services.

Of course, one solution is to have a main phone with a SIM, and a $60 Android for those services which require it. It can work, but it's not for everybody.