Comment by lxgr

There's Wi-Fi calling, but unfortunately at least in Germany, many operators don't support receiving SMS over that, unlike the US carries I've tried it with.

However, most banks/issuers have since switched to using their app as the second factor, so all you need is Wi-Fi, practically.

A few even support displaying an offline code in the app that you can enter during checkout, but that's becoming less common since it doesn't support displaying the amount and payee given how it works.