I've had a call from 1-000-000-0000. Also a call from something like 5p38@1 (I need to find that screen print I did that time one day -- it was kinda cool).
They're spam. Basically, they're "scare attempts" -- the 5p number tried to tell me my "Mastercard Express Account had suspicious activity and they needed info from me" (At least that was the recording on my voicemail). I obviously don't have a "Mastercard Express", so I didn't answer.
The other was someone claiming to be my antivirus software (really? I didn't have any AV software at the time... seriously!) claiming my computer was infected. http://www.youtube.com/watch?v=jb69H7l0vJA is another example of this.
The short is just ignore them.