I don't know this number either, received call on my T-Mobile and my home phone late October 2012 and today 11.13.12. When I answered the cell the caller did not speak. The caller did not leave a message on the home phone either.
Funny, I checked the callers info given by my phone when a few seconds empty voicemal was left, but the number is different. However, it appears as shown above in the missed call section.