BB 8830 WE is not the best choice if you travel to S.America because those countries often use US/Canadian GSM bands, which BB 8830 WE doesn't support (850/1900 MHz). Besides, it's an older model, with very low memory. I'm happy with mine, but I have tweaked it a lot and I don't have lots of apps on it.
The latest hybrid CDMA/GSM BlackBerry replacements for 8830 WE are 9630 and 9650. They support all four basic GSM bands (900/1800, 850/1900 MHz) and will work on any GSM network anywhere in the world (please double check the frequencies on RIM's website).
Any hybrid CDMA/GSM phone sold by Bell or Telus will have a SIM card pre-installed. To replace it with your own SIM (let's say from some S.American carrier) the phone would need to be "unlocked" by Bell/Telus. I paid full price for my BB and it was unlocked, it's just one way to do it.
If you buy a second hand phone there are other unlocking methods available.
GSM coverage maps are here:
GSM World Coverage Map- GSM Country List by frequency bands
These days, as Bell and Telus are not investing much in their old CDMA networks and slowly switching over to GSM, you will only need a hybrid CDMA/GSM phone ( BB 8830 WE, BB 9630 or 9650) in a few places on the planet where CDMA is still dominant, that is in N.Ontario, Manitoba, Saskatchewan, all three Territories, Japan and in the US outside big cities (were Verizon CDMA rules supreme).
If you don't need coverage in those places, then you might as well get a new fancy GSM phone from Bell, Telus or Rogers, just make sure that the phone supports all four frequency bands mentioned above.
I have also heard that lately you need to call Bell before going outside US/Canada and they will unlock overseas roaming.
And don't believe in any technical information provided by sales reps. They are mostly clueless about technical standards. There are some exceptions among them, and you can sometimes see them on these forums, but they are just that, exceptions. Before buying a new BB check technical specs on user forums and on RIM's website.
Posted from my CrackBerry at wapforums.crackberry.com