Personally I think there are possible federal wiretapping laws that might have something to say about a telecom that is offering an E2EE secure phone line to someone who is not on duty as a police officer (cop), federal agent (glowie), or other authorized federal, state or local employee (bureaucrat, with data that has legitimate need to be protected).

That's not even considering the entitled political hand-wringing about terrorists, spies, drug dealers, pedophiles and other so called "EVIL" people who "should not have access to such a powerful tool" because "it's our law enforcement's right to catch them in the act." Unfortunately it's a nuanced problem and we can't wave away all of that hand-wringing, even if we think most of it is dramatic and performative. They do have some points.

But...even if we were to suppose for a moment that all of the above issues are not a problem... because something likely happened to wake people up to the need for privacy...we would be facing an entirely new set of technical challenges to hurdle over.

As our current cell networks are structured; we would need to deploy cell phones with phone numbers that do not typically allow routing of outbound unencrypted calls...instead all phone calls would need to be routed over cellular data (AKA LTE or 5G). These calls could definitely be nominally routed by an existing application such as Signal and would require that remote recipients also install the Signal app to receive encrypted calls.

Essentially you'd have a phone which is a Data+SMS only line with a phone number for ease of access. You wouldn't be able to make outbound unencrypted calls or send SMS messages except to emergency services.