It's the number that's used by Cingular for voice mail.

I received 2 text messages, the phone# is the content of the text...

probably a telephone solicitor

The calls are annoying appearing on my cell- no message- just the
        number p0ps up-- Who is this terrible person--bothering people!!!?
            I will notify the police!!

It is the number for AT & T voicemail.  If you are calling for your messages from your cell, this is the number that will show.  I just changed my phone number due to harasing calls and this number pops up now.  Before it just said "voicemail" and I did not have to dial a number.  I just went to the "My stuff" folder and clicked on the voicemail.  No worries.

I don't have AT&T voicemail yet I get calls from this number that go directly into my phone's voicemail... No message or anything, however, as I have a TracFone and you buy minutes as needed, this is wasting my minutes.  Haven't been able to figure out how to completely block the number so my phone doesn't receive calls from this number.