Looks like good ole social engineering was behind the oh sooo publicized T-mobile sidekick hack of Ms. Hilton.

Computer security flaws played a role in the attack, which exploited a programming glitch in the Web site of Hilton's cell phone provider, Bellevue, Wash.-based T-Mobile International. But one young hacker who claimed to have been involved in the data theft said the crime only succeeded after one member of a small group of hackers tricked a T-Mobile employee into divulging information that only employees are supposed to know.

The young hacker described the exploit during online text conversations with a washingtonpost.com reporter and provided other evidence supporting his account, including screen shots of what he said were internal T-Mobile computer network pages. Washingtonpost.com is not revealing the hacker's identity because he is a juvenile crime suspect and because he communicated with the reporter on the condition that he not be identified either directly or through his online alias.
...
In the months leading up to the Hilton incident, the hacker group freely exploited a security glitch in the Web site of wireless phone giant T-Mobile, according to the hacker, who described himself as the youngest member of the group. The group had found that a tool on the T-Mobile site that allowed users to reset their account passwords contained a key programming flaw.

By exploiting the flaw, the group's members were able to gain access to the account of any T-Mobile subscriber who used a "Sidekick," a pricey phone-organizer-camera combination device that stores videos, photos and other data on T-Mobile's central computer servers.

Paris Hilton Hack Started With Old-Fashioned Con