OK, for you techies out there. Real life issue, no idea where to start. Client gets a phone call. Caller ID says it is from Bob, who had called just a few minutes earlier. Bob is a person known to client and is in the phone's contacts list. When client answers the phone, the call is NOT from Bob, but from someone obviously harassing, etc. Client hangs up and immediately calls back to the number that just called. Bob answers the phone, because it is Bob's number. We know that Bob didn't make the first call, because Bob was in the car with the client when all this happened? QUESTION: Anyone have any idea how this happens? Is this someone being able to spoof/copy another phone, or is this just a random hack job?
Chances are the fact that it was "Bob" whose number showed up right after talking to "Bob" is a fluke. Marketers are spoofing phone numbers now, have been for a while. Not sure exactly how they do it but essentially caller ID is all but worthless now. I've had a couple of calls from people to my cellphone who said their caller ID showed a missed call from me when I didn't call them. Probably 95% or more of the calls I receive these days are junk. Even if I recognise the number I usually let the voicemail take it because if it really is that person they'll leave a message and if it isn't they'll give up like the rest. Sadly it's not so easy to do that with a business phone because people expect an answer.
Number/caller ID spoofing most likely (it's extremely easy); a hack job is possible but would be more involved (has Bob misplaced his phone, had it stolen, etc.?). Unfortunately, both are very difficult to track down.