No, WiFi is not hard to do. If you use a little router connected to the Ethernet shield, for example a TP-Link TN Wr702n it is very simple. This is a little travel router that comes configured as an AP ( Access Point, or Hotspot). You can integrate it also into an existing network if you so desire.
You should be able to use any WiFi enabled phone to connect to it. I can verify that it works with an iPhone and iPad.
Once connected, or should be able to run any of the sample scripts that come with the Ethernet library and they should run without problems. The WiFi connection is transparent to the Ethernet shield.