My cellphone has a “screen this caller” feature. I get almost no spam on my cellphone (and very few calls of any kind) but when i have an incoming call from a number the phone doesn’t know, it asks if i want to screen the call. I say “yes”, it tells the caller that I’m screening calls and asks them who they are. They are almost always someone i want to talk to, and i can easily interrupt the screening to answer the phone.
So I’ve only used nomorobo on the land line, where i like it a lot. It does have some false positives. So the red cross and the woman calling me back about my employee benefits (who are both probably using call h center technology) get picked up. But the caller ID still works, and if I’m quick, i can answer the call before it gets disconnected.
The only false positive I’ve had is my college looking for money, which I’m usually happy to give them. NoMoRobo gives an option for a person to hit “1” or something to prove they’re not a robot, so I noticed the call got blocked and they called back right away.
My cellphone is better about identifying spam these days. It goes to voicemail and I often listen, and they’ve been right 100% of the time.
In fact, i see that I’ve tried doing it a few times in the past (texted “heading home” to my husband, but clicked the wrong phone number) and got no error message. And no text, of course.
It seems to be a function of your own carrier and various others downstream towards your destination.
If your carrier doesn’t support the landline error message, you’ll never see one. If your carrier does support landline error messages, you’ll often see them, but the absence of a message is no guarantee it got through, since you have no idea who else along the way did or didn’t do their part.