How do I block calls when there is no phone number?

You cannot on the iPhone. Unless there is a phone number coming from Caller ID, there is nothing to block. Some cellular carriers can block some of this at their end before it comes to your phone. Check with them, however understand that some of these features come with a cost.

You're welcome. It is easy for them to block the Caller ID, as well as their current work at spoofing numbers. They are generating numbers based on your location, to use a local area code and familiar number prefix in the hope of you picking up. This whole robo calling thing irritates me as well. For my home phone, I've added a tone to the beginning of my message that is supposed to let the robot believe they have reached a disconnected or non-working number. It is called a SIT (special information tone) tone. Difficult to do with with a mobile voicemail, but I'd be willing to try if I was getting a lot of them. I still have a land line at home, so my mobile phone does not experience as much of the robo calls.

I cannot answer that question, since I'm not a spammer. Generally if someone answers, I believe the call gets routed to a person, or the recording they are using. I couldn't understand it either, but that is what they do.

jamesbtex wrote:

I don’t see how in this case it does the sender any good because all it is, is a series of three beeps that repeats over and over. Hang up and it calls again in about 5 minutes.

This repeats itself three times.

What would be the purpose of just sending someone three beeps?

Maybe a fax machine.