This is where's my cell phone number. You call it; it rings your phone so you can "hurry find it!" It's a free service. Totally handy and harmless. I forgot I called it to find my phone. Then when I got my phone, I saw the "missed call" number. OOPS!!! Don't get excited. It's a very useful service. Google "wheresmycellphone" and you'll see it.
I'm amazed at all the people in this thread asking what this number is or how to make these calls stop, when they could easily find these things out if they spent 30 seconds reading any of the numerous posts on here from people explaining who this caller is.