Memory card slots are used primarily to add memory to a phone, in the form of a memory card. 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.

Some card slots also support cards with other functions, such as Wi-Fi connectivity or an NFC reader. In this way the card slot can be used to add features to a device. The most common standard for this capability is SDIO, which we list as a separate feature.

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.

The most common type of memory card in phones is microSD (as of 2012):