The problem: In 2004 the Secret Service captured an elusive California hacker who'd long stayed one step ahead of the agency's best sleuths. The hacker's secret? One of the agents had been receiving information about the probe on his Sidekick PDA, and the Secret Service didn't realize that T-Mobile's servers were easily penetrated. Paris Hilton learned the same lesson a few months later.

The solution: If you're unsure about your service provider's security procedures, bring your mobile e-mail server in-house. Research in Motion sells an enterprise server for its BlackBerry handhelds, and Windows Mobile 5-based devices can integrate directly with your Exchange server. Urban pickpockets are also a danger, so encrypt sensitive data stored on the device itself.