This video shows that it is entirely possible to find out who is calling you from a blocked phone number. It’s not an easy method and for someone without some technical know how, but pretty useful indeed. It involves using Asterisk and a SIP Trunk. For some of you this might be a fun project to try out, you will learn all about VOIP and PBXs.
Also of note: By using a third party caller spoofing service, your phone number will NOT show up if someone is using this method. By allowing your call to be placed on your behalf and connected to you with one of these services, your anonymity remains intact because only the real number of services’ outbound line would show up…if anything at all.