Is Claro (or Movistar) a MVNO (Mobile Virtual Network Operator) using AT&T infrastructure? If so then you may be able to safely load the firmware that you found.
You never did say what model and firmware you currently have, or why you want to load the AT&T firmware.
Frankly, people in your region would be the best resource - I've never heard of the provider that you have, and wouldn't want to steer you wrong.
All I can tell you is that Odin will allow you to load any firmware that you want - that doesn't mean that your phone will work when you're done. This isn't something to be taken lightly, or to 'fool around with'.
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM 10.2 using Tapatalk 4