Who called from 3187309198

Appears as a missed call on my phone at work.

Received a call from this number on my cell phone at work.  I don't answer calls from numbers I don't know.  They did not leave a message.

Just called me. I did not answer because I did not recognize the number. Left no message.

Received a call from this number this morning.  They caller did not leave a message.  I don't answer calls from area codes or numbers I do not recognize.

I said "hello" and a recording said "I'm sorry, that is not a recognized extension".  What the heck is that?