That or they will just credit you on your next bill. AT&T has been reidiculously good at crediting me for various things. I called last time because my mom (who is on our family plan) was using 411 (yeah... instead of just searching on the flipping web that her 4S is perfectly capable of doing) but I didn't know what the charges were. The charges amounted to about $10 over two months. They explained, I was happy with the explaination, but then decided to give me $84.71 credit. Don't ask me where they got that number from, but I wasn't about to ask!
I also got credited all kinds of money when the Lumia 920 launched. I basically got the phone for free, two chargers, and an EXTRA $200 towards my bill. It pays to call in every once in a while and be polite.