Expansion cards can be used to add memory or features to a phone. Extra memory can be used to store and transfer photos, videos, music, computer files, or backups of phone data such as the phone book and calendar.
There are several different types of cards. Each has a different shape and size, but cards from a phone can also be used with other devices which use the same type of card. Such devices might include handhelds, digital cameras, and MP3 music players.