Who called from 4230000000

Has been calling lately with no id and no vocal response when answering the phone.

Just called.....no response when I said hello.

CID says name not found. I answer anyway, knowing that there is no such real phone number. "Hello", pause, dead air, "you didn't really call to talk to me, did you?' Click, dial tone.
I've given up trying to figure out who or why such calls are made.