Yes. Witches and Wizards can apparate anywhere in the world, although many private residences (including Hogwarts) are protected by "Anti-Apparating Spells." This, however, has no effect on magical creatures such as Phoenixes and House-Elves.
Rhr4eva's answer: I just thought I would add that yes, indeed they can. Harry, Ron, and Hermione do so quite a few times in Deathly Hallows, while theye're on the run.
Apparition is not restricted by distance, however, as the distance increases, the difficulty of success increases. Theoretically, one could apparate anywhere on in or around the Earth, but the chances of splinching ones self increase dramatically. Even Dumbledore and Voldemort were uncomfortable with apparition over long, international distances, in which case, they flew. Dumbledore by Thestral, and Voldemort using the unique spells he invented for true unaided flight, a feat that, until he managed it, was thought impossible.