I think its some type of generic number when people use a calling card. My friend (who doesn't have a cell or long distance on house phone) left a message on my voicemail following the missed calls from this number
This number came up for me when a friend was calling me...I answered the call not recognizing the number but expecting a call from him and it was in fact him on the line and he was calling me from the phone at his work and when I asked him the number he indicated that was not their number and not even a number he'd ever heard of