Who called from 317317

I have recieved two calls from 317-317 they were a couple months apart and they were actual calls to my cell phone not text messages, what the heck kind of number is this?! The first call I let got to my voicemail and they didnt leave a message and the 2nd call I answered and only heard them hang up.

Also this shows up on my verizon bill as a call from 999999999

I got a call on my cell from this number too on 10/28/09 @ 7:59 CST.  They did not leave a voice mail.

I got a call from them too at 8am eastern and did not leave a message.

Just called me today - 6/2/2011

This is very strange