Just sharing experience with the XBee WiFi modules and Arduino. The WiFi modules are mechanically bigger; they don’t fit on the carrier boards from Sparkfun and Adafruit wihtout some modification.
“Mechanically bigger” means that they’re longer and have a higher height. The metal “box” on the underside of the module is higher which causes conflict with some carrier boards that have components mounted between the two 1 x 10 headers for the XBee module.
I have to change the vertical 0.1" header (i.e. the one that connects to the Arduino) on my Sparkfun board to a right angle header so that the XBee fits. I was just building the Adafruit kit when I got the WiFi modules so I “raised” the 1 x 10 headers as high as possible (instead of pressing tightly to the PCB) and the WiFi modules would fit above the DIP on the Adafruit board.
Next problem was that the Sparkfun board power supply filtering was inadequate and WiFi module would only initialize maybe 1 in 20 attempts. I found the WiFi module datasheet has a much more stringent requirements on power supply filtering. I modified the Sparkfun (and Adafruit) boards with additional capacitors as suggested by datasheet and they now work fine. Three capacitors were added – a large 500 uF capacitor to handle the initial power surge on startup and two small values to better filter high and medium frequency noise; specific values are recommended in Digi’s data sheet.
Hope above saves others some grief.