Do you know from current experience that a blocked phone number can leave a voicemail message?

That is not my experience and would be somewhat contrary to the whole concept of "block".


On a Mac since 1984.
Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.