They provide free data-only sim cards. And you used to be able to sync all of your texts and calls in the hangout app, but they got rid of that. The last time I tried syncing the Messages app to a data o my device, it didn't work too well. That was a while ago though so not sure if that is still the case.
Swapping sim cards is probably too much of a hassle. You could just make the epaper phone your primary, and drag along the second phone as needed. Also, there is no reason an epaper phone can't take photos. Plenty of camera gear out there where the viewfinder/preview screen is a very poor preview of the final image and regardless, most folks just snap away with their phones and look at the images later. Modern smartphones do most of the work regarding camera settings.
Swapping sim cards is probably too much of a hassle. You could just make the epaper phone your primary, and drag along the second phone as needed. Also, there is no reason an epaper phone can't take photos. Plenty of camera gear out there where the viewfinder/preview screen is a very poor preview of the final image and regardless, most folks just snap away with their phones and look at the images later. Modern smartphones do most of the work regarding camera settings.