Even if it ships worldwide, as somebody mentioned, how can one tell whether it actually works with <random carrier in country X>?

There's no doubt a lot of coarse-grained commonality between different carriers in different countries, but there also seem to be many differences when you get down to the details, and a lot of incentive to add gratuitous minor incompatibilities for the purpose of locking in your customers... I'd be pretty nervous about importing a random phone.