use v5.16;

package Example::Phone {
	use Moo;
	has number => (is => 'ro', required => 1);
	sub call { ... }
	
	# Make final
	sub BUILD {
		my $self = shift;
		die(sprintf '%s is final; %s cannot inherit', __PACKAGE__, ref($self))
			unless ref($self) eq __PACKAGE__;
	}
}

package Example::Phone::Mobile {
	use Moo;
	extends 'Example::Phone';
	sub send_sms { ... }
}

my $number1 = Example::Phone->new(number => 1);
my $number2 = Example::Phone::Mobile->new(number => 2); # dies