Phones are required, insering a SIM isn't. Your work and home probably have wifi, and services meant to be used on the go are commonly built with offline use in mind. Especially those you actually need in society
A burner phone left at home just for the ability to receive SMS would be helpful for account registrations though
> services meant to be used on the go are commonly built with offline use in mind.
I'm not sure about this. With everyone moving to the cloud and web applications, this seems to not have been the case for a while to me. There surely are what are now called "local-first" alternatives to the main services (in the past those would just be called desktop applications), but if someone is using Office 365, does it have an offline mode? (Sincerely asking since I never tried this, plus, you should still get to load the web application before losing connection, right?)
Depends on how you define a phone. Cell phones are not required but SMS capable phone numbers kind of are.
I ported my cell phone number to a voip provider and get SMS and can even take calls from my desktop, or laptop, or simple voip capable DECT phones around my home as needed.
A burner phone left at home just for the ability to receive SMS would be helpful for account registrations though