Will AT&T charge me for using my blackberry in Guatemala?

Ok so I just arrived at Guatemala and turned my Blackberry Torch on and noticed that I have signal. The weird thing is that the signal is no longer at&t but now it is a service called "claro" and so i was wondering if I can use this service without being charged? Plz can i get a serious answer and quick cause i wanna know if i can use it or not.