The Expansion Pack System allows users to add functionality on the fly by sliding on Expansion Packs on the back of the iPAQ Pocket PC. This enables users to add industry standard PC and CF Cards to their iPAQ Pocket PC. The Expansion Pack System has two types of Packs, including Expansion Packs (which have specific functionality) and Style Packs (which are cosmetic covers without electrical capabilities).With a Dual-Slot PC Card Expansion Pack, you have twice the functionality at your fingertips. You can use cards that will increase the file storage space on your iPAQ Pocket PC, access your company's wireless network (WLAN) for e-mail and Web browsing, access the Internet wirelessly through the cellular phone system. The Dual-Slot PC Card Expansion Pack also provides twice as much battery power as the PC Card Expansion Pack to run your PC Cards or to extend the life of your iPAQ Pocket PC between charges.