Roaming International

Hello, So I have an iPhone 6s, and I am on a $45 ATT Prepaid monthly. However, I am traveling to Guyana, which is the Caribbean, but it is in South America. I need to be able to have data and voice access, however, I can't figure out the proper way to go about this. I know that AT&T offers to roam to Guyana, being that ATT & GTT in Guyana is paired, However, I need assistance in what to do and if I can actually roam in Guyana. It would be a shame if I can roam on a regular ATT plan but not my prepaid, when I pay extra for roaming regardless.