Smart phone carriers and worldwide purchases, worth it?

I see a lot of smart phones being sold on ebay that have "Verizon" or "Sprint" listed as carrier. Does that mean that someone from a 2.5th world country like Croatia isn't able to use those unless he unlocks/jailbreaks them (provided those carriers don't exist here)? I would buy one here, but none of our carriers have them on offer, and I fear it may be years before the good ones come here.