to re-post this elsewhere. I'm not sure if you are talking about an iPad, a tablet, a notebook cell phone, or something else, so I can't suggest any specific forums.
If you look at the forum sections listed here; CNET Forums maybe you can find one for yourself, but if not, try the "Electronics" listings and iPhones & iPad forum, or similar.
Failing that, Computer Help.
My first thought, if you have subscribed to an ISP in the US, then you will not be able to access the internet using that same ISP anywhere else in the world. That is not just US ISPs, but any nation's ISPs. They are not international.
However, if you have an email account with your ISP and that account is available through a web browser, (web mail), as well as through email client software installed on your computer, then your emails are available anywhere in the world through an internet browser. Or if you use one of the web-based email services like Hotmail, Yahoo Mail, and so on, you will be able to access those via a browser throughout the world.
Scratch that; 'anywhere in the world'. I suspect some countries may impose limitations, for example China was in conflict with Google a while ago, and may still be.
An iPad should be able to pick up wireless 'hotspots' anywhere in the world, as should most wireless capable computers.
I have no idea about phones.
Is there a pad or a pod or even a phone that, if bought in the USA, would work the same in South Africa using the same ISP, email etc. ??