Just received call from this number.  I did not answer since I was not familiar with the 121 area code.

I got the same thing. My guess is that there is a phone number 1-215-253-881x where somehow the last digit gets cut off. If someone really wanted to, they could make 10 calls, supplying the last digit and grilling each one that answers the phone. I don't have time for this kind of detective work.

Happy grilling,
Federico

The same thing happened to me.  I answered, and there was no response.  It only happened the one time.

Same thing happened to me today. Called and nothing.

just calls and hangs up; like a sicko perv.