I've been looking on Wikipedia to try and figure this out, but I'm not much closer.

As far as I can tell, GSM is for overseas only?

What is the difference in speeds between EDGE, EVDO, CDMA, GPRS? Are they even the same thing?

I'm trying to decide whether to get a BB 8310 or a BB 8830. I use Sprint, and they don't offer me a 8310, so I'd have to change carriers and pay penalty.

Is the 8830 plenty fast? I don't plan on streaming video and such. I just want to browse the internet and IM/Text.