Answered by Stephanie, Hiring Expert at AT&T Inc., on Wednesday, December 16, 2015
The smart move is to seek out the best candidate for the position. This may mean internal and external candidates are being considered. So there is no sure fire way to know that a position will go to an external candidate over an internal candidate. However, if it posted in a public space, it is open to external candidates.
Another way to think about this is that if you are a fantastic, qualified candidate and you apply for a position, you just got your name/info in front of a recruiter. So even if an internal candidate is selected, you just made it possible you would be considered for other open positions.
Best of luck in your search!