After seeing 800-444-4444 mentioned in another thread I'd thought I'd try it out.

I called it 5 times in a row.

1st call, it identified my number as 319-228-9999

2nd call, identified my correct number

3-5, it identified my number as 319-228-9999

This explains why sometimes when I call my dad, his AT&T privacy protection blocks my call from going through.