The copy could state more explicitly that it does work as a regular phone with your number and SIM, but it is explained under the section "A No-Carrier Phone?":

The copy could state more explicitly that it does work as a regular phone with your number and SIM, but it is explained under the section "A No-Carrier Phone?": The Librem 5 can be used in any of three ways: - With a cellular carrier provided phone number, data plan, and WiFi - With a cellular carrier data plan, and WiFi - With no carrier, and using only WiFi WiFi calling and VoIP calling will be able to be provided in WiFi or data plan modes. We expect to offer call-out, and call-in with phone numbers in all of these plans as well. If you still require a “traditional” phone number through a carrier and want to make unencrypted phone calls or messaging, it will be an option you can choose, but is not required (we recommend avoiding unencrypted phone calls).