As the name implies, the Arduino Wireless SD shield serves two functions. Foremost, this shield allows you to easily interface with Xbee transceiver modules to create mesh networks, and other wireless devices. Secondly, the micro SD socket allows you to store and access a large amount of data. Whether using these functions by on their own or together, this chip greatly enhances the capabilities of a standard Arduino.
The Wireless SD shield allows an Arduino board to communicate wirelessly using a wireless module. It is based on the Xbee modules from Digi, but can use any module with the same footprint. The module can communicate up to 100 feet indoors or 300 feet outdoors (with line-of-sight). It can be used as a serial/usb replacement or you can put it into a command mode and configure it for a variety of broadcast and mesh networking options. The shields breaks out each of the Xbee's pins to a through-hole solder pad.
Included on board is a SD card slot. When using the SD Library to access the card, Pin 4 is CS and cannot be used otherwise. SPI also relies on pins 11, 12, and 13 for communication.
An on-board switch allows the wireless module to communicate with the USB-to-serial converter or with the microntroller.